Distortion compensating circuit

ABSTRACT

A distortion compensating circuit is provided in which, in the polar modulation system, while suppressing increase of compensation data and increase of the circuit scale, a modulated signal can be correctly expressed, or low-distortion characteristics of a power amplifier can be realized. Based on a steady characteristic compensating circuit  11  which stores an output signal amplitude and output phase characteristics with respect to a control voltage in a steady state, amplitude adjustment is executed on amplitude information r 11 (t) on which amplitude correction is performed, by a first amplitude information adjusting portion  13 , whereby the output-response characteristics of an output signal amplitude of an amplifier with respect to a change of the control voltage can be improved.

TECHNICAL FIELD

The present invention relates to a distortion compensating circuit whichcompensates distortion of an output signal of an amplifier that drives acontrol voltage to control the amplitude of the output signal withrespect to a predetermined amplitude of an input high-frequency signal.

BACKGROUND ART

In a recent mobile phone service, a demand for data communication inaddition to a voice call is increasing, and hence improvement of thetransmission speed is important. In the GSM (Global System for Mobilecommunications) system which is in widespread use mainly in Europe andAsia, for example, a voice call is conventionally performed by the GMSKmodulation in which the phase of a carrier is shifted in accordance withtransmission data. However, the EDGE (Enhanced Data rates for GSMEvolution) system has been proposed in which also data communication isperformed by 3π/8 rotating 8-PSK modulation (hereinafter, abbreviated to8-PSK modulation) in which bit information per symbol is enhanced bythree times as compared with the GMSK modulation by shifting the phaseand amplitude of a carrier in accordance with transmission data.

In a linear modulation system involving amplitude variation, such as the8-PSK modulation, a request for linearity of a power amplifier of atransmitting portion of a radio apparatus is severe. Usually, the powerefficiency in a linear region of a power amplifier is lower than that ina saturation region. When the related quadrature modulation system isapplied to a linear modulation system, therefore, it is difficult toimprove the power efficiency.

Therefore, a system which is called the EER method (Envelope Elimination& Restoration) or the polar modulation system, and in which improvementof the power efficiency of a power amplifier is realized by a linearmodulation system is known (for example, see Non-patent Reference 1). Inthe system, a transmission signal is separated into a constant-amplitudephase signal and an amplitude signal, phase modulation is applied by aphase modulator on the basis of the constant-amplitude phase signal, aconstant-amplitude phase-modulated signal having a level at which apower amplifier operates in saturation is input, and a control voltageof the power amplifier is driven at high speed, thereby synthesizingamplitude modulation. Hereinafter, in order to clarify that themodulation system is different from the quadrature modulation system,the system is referred to as polar modulation system.

FIG. 26 is a view which is obtained by extracting and plotting a 200 to400 [μs] portion in one time slot (577[μs]) of the GSM relating to anamplitude signal in the 8-PSK modulation. In FIG. 26, the abscissaindicates the time elapsed after the start of the time slot, and theordinate indicates the amplitude of the amplitude signal.

FIG. 27 is a view which is obtained by plotting passing phasecharacteristics in the case where a control voltage which is graduallychanged (monotonically increased or decreased) with respect to theelapse of time is applied to a power amplifier. In FIG. 27, the abscissaindicates the normalized control voltage, and the ordinate indicates thepassing phase rotation amount with reference to the normalized controlvoltage of 1. The solid line in the figure shows passing phasecharacteristics in the case where the normalized control voltage isgradually changed in monotonic increase from a low voltage (0) to a highvoltage (1) (rising characteristic), and the broken line in the figureshows passing phase characteristics in the case where the normalizedcontrol voltage is gradually changed in a monotonic decrease from thehigh voltage (1) to the low voltage (0) (falling characteristic). Boththe solid and broken lines show the case where an input high-frequencysignal amplitude (the same value) having a level at which the poweramplifier operates in saturation is supplied.

In the polar modulation system, a constant-amplitude phase-modulatedsignal is input to a power amplifier, and hence the power amplifier canbe used at the saturation operating point. This is advantageous from theviewpoint of the power efficiency. In order to express an amplitudesignal such as shown in FIG. 26 in which a point of pole inflection ofthe maximum value and the minimum value of the amplitude exists within 2[μs], however, the control voltage of the power amplifier must be drivenat high speed. Because of differences in charging and discharging tomeswith respect to the capacitance (including the parasitic capacitance) ina control-voltage input portion of the power amplifier, even when thechange width of the control voltage has the same value, the phase changeamount is different in the cases where, as shown in FIG. 27, theconditions of application of the control voltage change from the lowvoltage to the high voltage, and where the conditions change from thehigh voltage to the low voltage. Namely, the phase characteristicschange at the signal change point. Therefore, a technique for improvingthe output-response characteristics of the power amplifier with respectto the input control voltage (a technique for linearizing an output) isrequired.

Next, in the GSM system, the radius of a cell to be covered by a basestation is large, and hence the specified value of the maximumtransmission power for a mobile station transmitting apparatus is high.In order to reduce the power consumption of the mobile stationtransmitting apparatus, therefore, the transmission power of the mobilestation transmitting apparatus is controlled in accordance with thedistance between a base station and a mobile station. For example, FIG.28 is a view showing a transmission power regulation for a mobilestation transmitting apparatus. In the figure, the power control levels5 to 31 in the case where a mobile station transmitting apparatuscorresponding to the GSM 900 MHz band transmits an 8-PSK modulated waveare excerpt from power control levels of a transmission power regulationin uplink to a mobile station transmitting apparatus stipulated in GSMstandard “Digital cellular telecommunications system (Phase 2+); Radiotransmission and reception (3GPP TS 05.05 version 8.9.0 Release 1999)”.In the 8-PSK modulation, power classes E1 to E3 are maximum outputpowers, and a power control is performed on an output power which isequal to or lower than them.

In the polar modulation system, as means for performing the powercontrol, usually, the control voltage of the power amplifier is adjustedso as to attain a desired output power.

In the polar modulation system, however, the amplitude of an inputhigh-frequency signal to the power amplifier is set to be large so thatthe operating point of the power amplifier is in the saturation region.In the case where the output signal amplitude is suppressed by adjustingthe control voltage, therefore, the depletion layer capacitance betweenthe base and collector terminals of a transistor constituting the poweramplifier is increased, and leakage components of the inputhigh-frequency signal are increased. Due to the leakage components,there arise problems in that the output signal amplitude cannot bereduced to a predetermined value or smaller, and that the passing phaseamount is largely changed.

Therefore, also a technique for linearizing the output of the poweramplifier when the transmission power is reduced is required.

From the above, in the polar modulation system, a technique forcompensating the nonlinearity of a power amplifier due to that thecontrol voltage is driven at high speed, and that the transmission poweris controlled by using a saturation power amplifier is required. Next,the related art relating to the compensating technique will bedescribed.

(Related Art 1: Predistortion Type Distortion Compensating Technique inQuadrature Modulation System)

As a related art example of a technique for linearizing the output of apower amplifier in which a control voltage has a constant value and isin a steady state, there is a predistortion type in which amplitude andphase distortions occurring in the power amplifier under theabove-mentioned conditions are previously measured, and correction usinginverse characteristics of the distortion is previously performed on aninput signal of the power amplifier, thereby obtaining an output signalamplitude and passing phase characteristics which are desired (forexample, see Patent Reference 1).

FIG. 29 is a view showing output signal amplitude characteristics(AM-AM: Amplitude Modulation to Amplitude Modulation conversion) andpassing phase characteristics (AM-PM: Amplitude Modulation to PhaseModulation conversion) with respect to an input high-frequency signalamplitude of a power amplifier in which a control voltage has a constantvalue and is in a steady state, and FIG. 30 is a block diagram showing aschematic configuration of a related predistortion type modulatingapparatus described in Patent Reference 1. Hereinafter, irrespective ofthe kind of an input signal, for a change of an output signal occurringin accordance with a change of the input signal amplitude, a change ofthe output signal amplitude is referred to as AM-AM characteristics, anda change of the output signal phase is referred to as AM-PMcharacteristics.

In FIG. 29, the abscissa indicates the amplitude of the inputhigh-frequency signal, the ordinate (left) indicates the amplitude ofthe output signal, and the ordinate (right) indicates the phase rotationamount (passing phase) of the output signal with reference to the inputhigh-frequency signal. The solid line in the figure shows a graph whichis obtained by plotting the AM-AM characteristics with respect to theinput high-frequency signal amplitude, and the broken line in the figureshows a graph which is obtained by plotting the AM-PM characteristicswith respect to the input high-frequency signal amplitude.

As shown in FIG. 30, the related predistortion type modulating apparatushas a memory 2901, IQ-signal correcting means 2902, and a quadraturemodulator 2903. The memory 2901 stores the AM-AM and AM-PMcharacteristics with respect to the input IQ-signal amplitude.

Here, correspondence relationships between the AM-AM and AM-PMcharacteristics as shown in FIG. 29 with respect to the inputhigh-frequency signal amplitude of the power amplifier, and the AM-AMand AM-PM characteristics with respect to the input IQ-signal amplitudewill be described.

The output amplitude of the quadrature modulator 2903, i.e., the inputhigh-frequency signal amplitude of the power amplifier which is notshown is changed in accordance with the input IQ signal (not restrictedto have a constant amplitude) transmitted from a baseband signalgenerating portion which is not shown. Therefore, correspondencerelationships between the input IQ-signal amplitude and the outputsignal amplitude of the quadrature modulator 2903 (the inputhigh-frequency signal amplitude of the power amplifier) are obtained.Furthermore, the AM-AM and AM-PM characteristics as shown in FIG. 29with respect to the input high-frequency signal amplitude of the poweramplifier in which the control voltage has a constant value and is in asteady state are obtained. Such characteristics of a power amplifier canbe easily acquired by using a network analyzer and the like, asdescribed in “Measurement of AM/AM and AM/PM Characteristics” p. 63,paragraph 2.13.4 of Non-patent Reference 1.

Next, based on the AM-AM characteristics of the quadrature modulator2903 with respect to the thus acquired input IQ signal amplitude, andthe AM-AM and AM-PM characteristics of the power amplifier with respectto the input high-frequency signal amplitude which are acquired asdescribed above, the AM-AM and AM-PM characteristics with respect to theinput IQ signal are acquired. Then, the AM-AM and AM-PM characteristicsare stored as the absolute values, or as a predetermined value(difference value) which is acquired by multiplying or dividing theinput IQ-signal amplitude by a predetermined value and then normalizingthe resulting value with the input IQ-signal amplitude so as to attainthe absolute values.

In accordance with the input IQ signal, then, an amplitude/phasecorrection signal which becomes inverse characteristics of the AM-AM andAM-PM characteristics is output to the IQ-signal correcting means 2902.In the data stored in the memory 2901, the input IQ signal may benormalized with the maximum value of the amplitude component after polarcoordinate conversion, and an address number may be assigned to each ofpredetermined amplitude steps.

The IQ-signal correcting means 2902 executes correction on the input IQsignal based on the amplitude/phase correction signal.

The quadrature modulator 2903 executes quadrature modulation based on asignal output from the IQ-signal correcting means 2902.

In this way, a modulated signal which is previously distorted inconsideration of inverse characteristics of the input/outputcharacteristics of a power amplifier is affected by actual amplitude andphase distortions occurring in the power amplifier so as to have anoutput amplitude and a phase which are desired, whereby the linearitycan be improved.

(Related Art 2: Predistortion Type Distortion Compensating Technique inPolar Modulation System)

As a related art example of a technique for linearizing the output of apower amplifier in the polar modulation system in which the controlvoltage of a power amplifier does not have a constant value and is notin a steady state, and amplitude modulation is executed by driving thecontrol voltage of a saturation power amplifier at high speed, there isa technique in which the anti-control voltage characteristics of theoutput signal amplitude and passing phase in a predetermined saturationpower amplifier which are previously acquired, with respect to apredetermined input high-frequency signal amplitude are accumulated in amemory, and the memory is referred to execute predistortion typedistortion compensation (for example, see Patent Reference 2).

FIG. 31 is a block diagram showing a related polar modulating apparatusto which the predistortion type distortion compensation described inPatent Reference 2 is applied.

As shown in FIG. 31, the polar modulating apparatus comprises: a poweramplifier 3000; polar coordinate converting means 3001; a memory 3002;an amplitude controller 3005 which has amplitude information correctingmeans 3003 and amplitude modulating means 3004; and a phase-modulatedsignal generator 3008 which has phase information correcting means 3006and phase modulating means 3007.

The polar coordinate converting means 3001 separates an IQ signal inputfrom a baseband signal generating portion which is not shown, into anamplitude signal r(t) and a phase signal θ(t) having a constantamplitude.

The memory 3002 stores output signal amplitude characteristics andpassing phase characteristics with respect to an input control signal ofthe power amplifier 3000 at a predetermined input high-frequency signalamplitude, and outputs an amplitude correction signal and a phasecorrection signal which become inverse characteristics of the poweramplifier 3000, in accordance with the input amplitude signal r(t).

The amplitude information correcting means 3003 performs correction onthe input amplitude signal r(t) based on the amplitude correction signaloutput from the memory 3002.

The amplitude modulating means 3004 drives at high speed the controlvoltage of the power amplifier 3000 based on an output signal of theamplitude information correcting means 3003.

The phase information correcting means 3006 executes correction on theinput phase signal based on the phase correction signal output from thememory 3002.

The phase modulating means 3007 performs phase modulation based on anoutput signal from the phase information correcting means 3006.

Although not described in the specification of Patent Reference 2, thedata to be stored in the memory 3002 are data in the absolute valueformat of the AM-AM and AM-PM characteristics in which the inputhigh-frequency signal amplitude of the power amplifier in the abscissaof FIG. 29 is replaced with the input control signal amplitude, or apredetermined value (data in the format of a difference value) which,after the input control signal amplitude is multiplied or divided by theabove-mentioned predetermined value, is normalized with the inputcontrol signal so as to attain the absolute value.

In this way, an amplitude-modulated signal and a phase-modulated signalwhich are previously distorted in consideration of inversecharacteristics of the output characteristics of a power amplifier withrespect to an input control signal are affected by actual amplitude andphase distortions occurring in the power amplifier so as to have anoutput amplitude and a phase which are desired, whereby theoutput-response characteristics (linearity) with respect to an inputcontrol voltage can be improved.

(Related Art 3: Technique for Improving Output-Response Characteristicswith Respect to Input Control Voltage in Power Amplifier)

As a related art example of a technique for improving theoutput-response characteristics with respect to an input control voltagein a power amplifier, there is a technique in which the level of aninput high-frequency signal to the power amplifier is controlled inconjunction with adjustment of the control voltage of the poweramplifier, thereby suppressing overshoot of an output signal withrespect to the control voltage (for example, see Patent Reference 3).

FIG. 32 is a view showing output signal amplitude characteristics of apower amplifier with respect to an input control voltage, and FIG. 33 isa block diagram showing means (transmission power controlling circuit)for improving output-response characteristics with respect to thecontrol voltage in the related power amplifier described in PatentReference 3.

In FIG. 32, the abscissa indicates the control voltage, and the ordinateindicates the output amplitude. As indicated by the broken line in thefigure, when, at the same output amplitude, the amplitude of an input ofthe power amplifier is suppressed in the direction of the arrow, thesensitivity (inclination) of the output signal amplitude with respect tothe control voltage is moderated.

As shown in FIG. 33, the transmission power controlling circuitcomprises a variable-output amplifier 3201, a power amplifier 3202, asignal input terminal 3203, a signal output terminal 3204, a controlterminal 3205 of the variable-output amplifier 3201, and a controlterminal 3206 of the power amplifier 3202.

When, under conditions that the amplitude of an input high-frequencysignal of the input terminal 3203 and an input voltage of the controlterminal 3206 are constant, an input voltage of the control terminal3205 is adjusted so that the amplitude of an output signal from thevariable-output amplifier 3201 is suppressed, the sensitivity of theoutput amplitude of the power amplifier 3202 with respect to the controlvoltage can be suppressed because of the relationship of FIG. 32. Whenthe input voltages of the control terminals 3205, 3206 aresimultaneously adjusted, therefore, the sensitivity of the output signalamplitude with respect to the control voltage, for example, overshootcan be suppressed.

(Related Art 4: Technique for Compensating AM-PM Characteristics atSignal Change Point)

As a related art example of a phase compensating technique forcompensating a change of the AM-PM characteristics at a signal changepoint of an input control signal of a power amplifier, there is atechnique in which the output signal amplitude of the power amplifier isdetected, the detection signal is differentiated to obtain a signalchange point, and thereafter a synchronizing timing between an amplitudesignal and a phase signal is adjusted in order to compensate a change ofthe AM-PM characteristics at the signal change point.

FIG. 34 is a block diagram showing a related apparatus forphase-compensating at a signal change point described in PatentReference 4.

As shown in FIG. 34, the phase compensating apparatus comprises: thepower amplifier 3000, digital-analog converting circuits 3301, 3302, areference clock 3303, amplitude modulating means 3304, phase modulatingmeans 3305, a change-point detecting circuit 3306, and delaying means3307.

The digital-analog converting circuit 3301 converts an IQ signal (I, Q)in a digital format input from a baseband signal generating portionwhich is not shown, to an IQ signal in an analog format.

The digital-analog converting circuit 3302 converts an amplitude signal(r) in a digital format extracted from the IQ signal (I, Q) in a digitalformat by polar coordinate converting means which is not shown, into anamplitude signal in an analog format.

The reference clock 3303 supplies a clock signal which serves as areference of the converting operation, to the digital-analog convertingcircuits 3301, 3302.

The amplitude modulating means 3304 drives at high speed the powersource voltage of the power amplifier 3000 based on the amplitude signalin an analog format.

The phase modulating means 3305 produces a phase-modulated signal basedon the IQ signal in an analog format, and outputs the signal to thepower amplifier 3000.

The change-point detecting circuit 3306 differentiates the output signalof the power amplifier 3000, and then detects a signal change pointbased on the sign of the differentiation value.

The delaying means 3307 adjusts, at the signal change point detected bythe change-point detecting circuit 3306, converting timings of thedigital-analog converting circuits 3301 and 3302, i.e., synchronizationbetween the amplitude signal and the phase signal which are extractedfrom the IQ signal.

In this way, synchronization between the amplitude signal and the phasesignal is adjusted at the signal change point, whereby the phase changeamount can be controlled.

When the delay amount is adjusted based on the sign of thedifferentiation value, therefore, the phase change amount at the signalchange point can be controlled.

(Related Art 5: Technique for Improving Output-Response Characteristicsof Power Amplifier when Transmission Power is Reduced, with Respect toInput Control Voltage)

As a related art example of a technique for linearizing the output of apower amplifier when the transmission power is reduced, there is atechnique in which a variable-output amplifier is connected to a frontstage of the power amplifier, and, when the output signal amplitude ofthe power amplifier is to be reduced, also the gain of thevariable-output amplifier is reduced, so that the amplitude of an inputhigh-frequency signal of the power amplifier is suppressed (for example,see Patent Reference 5).

FIG. 33 is a block diagram showing low-output linearizing means in therelated power amplifier described in Patent Reference 5.

FIG. 35 is a view showing passing phase characteristics of a usual poweramplifier with respect to a control voltage (steady state). In FIG. 35,the abscissa indicates the normalized control voltage, and the ordinateindicates the passing phase rotation amount with reference to thenormalized control voltage of 1. The solid line in the figure showspassing phase characteristics in the case where an input high-frequencysignal amplitude Pin of the power amplifier is Pin=P1, and the brokenline in the figure shows passing phase characteristics in the case whereinput high-frequency signal amplitude Pin of the power amplifier is P1n=P2 (<P1). During measurement of the passing phase characteristics, Pinhas a constant value.

As shown in FIG. 35, in order to suppress a change of the passing phasecharacteristics in a region where the control voltage is low, it iseffective to reduce the amplitude of the input high-frequency signal ofthe power amplifier. Furthermore, reduction of the amplitude of theinput high-frequency signal of the power amplifier is effective insuppression of a power of input high-frequency signal components leakingto the output terminal in the region where the control voltage is low.

Therefore, for example, a case where the input voltage of the controlterminal 3206 is reduced and the output power of the power amplifier3202 is reduced will be considered.

When the input voltage of the control terminal 3206 is lowered, it ispossible to suppress the amplitude of the output signal from thevariable-output amplifier 3201, i.e., the amplitude of the inputhigh-frequency signal of the power amplifier 3202, and reduce leakagecomponents of the input high-frequency signal, i.e., suppress the outputsignal amplitude to a predetermined value or less. Because of therelationship of FIG. 34, the change width of the passing phase amountduring a low-output power period of the power amplifier when the controlvoltage is low can be suppressed.

Patent Reference 1: JP-A-61-214843 (FIGS. 3 and 10)

Patent Reference 2: JP-T-2004-501527 (FIG. 11)

Patent Reference 3: JP-A-5-152977 (FIGS. 1 and 4)

Patent Reference 4: JP-T-2002-530992 (FIG. 2)

Patent Reference 5: US 2002-0177420 A1 (FIG. 2)

Non-patent Reference 1: Kenington, Peter B, “High-Linearity RF AmplifierDesign”, Artech House Pulishers (p. 162, FIG. 4.18)

DISCLOSURE OF THE INVENTION Problems that the Invention is to Solve

In the polar modulation system, in order that a control voltage of apower amplifier is driven at high speed and an amplitude signal of atransmission signal is correctly expressed, it is required to considertransient response characteristics in a period from switching of thecontrol voltage to a timing when the output level of the power amplifierbecomes to a desired level.

Moreover, in the polar modulation system, in order that a controlvoltage of a power amplifier is driven at high speed and an amplitudesignal of a transmission signal is correctly expressed, it is requiredto compensate a change of the AM-PM characteristics at a signal changepoint of the control voltage.

Furthermore, in the polar modulation system, a saturation poweramplifier is used. In order that, when the transmission power isreduced, the change width of the passing phase amount with respect tothe output signal amplitude is suppressed, therefore, it is required toreduce leakage components of the input high-frequency signal.

For items which are required for realizing such a polar modulationsystem, problems which remain to be solved in the related art will bedescribed.

In the output linearizing technique for the related power amplifierwhich is shown in related art 1, and in which the control voltage has aconstant value and is in a steady state, the case where the controlvoltage is in a steady state is assumed. In order to apply the techniqueto the polar modulation system, it is required to store in the memory anoutput signal amplitude and passing phase characteristics with respectto the time elapsed after switching of the control voltage, and a changeamount of the passing phase corresponding to increase or decrease of thecontrol voltage, in addition to the output signal amplitude and thepassing phase characteristics with respect to an input high-frequencysignal in the case where the related control voltage is in a steadystate. Therefore, there is a possibility that compensation data arelargely increased.

In the output linearizing technique for the related power amplifierwhich is shown in related art 2, and in which the control voltage of thepower amplifier does not have a constant value and is not in a steadystate, and amplitude modulation is executed by driving the controlvoltage of a saturation power amplifier, a distortion compensatingmethod which can suppress increase of compensation data whileconsidering the output signal amplitude and the passing phasecharacteristics with respect to the time elapsed after switching of thecontrol voltage, and a change amount of the passing phase correspondingto increase or decrease of the control voltage is not disclosed. In thesame manner as the case where related art 1 is applied to the polarmodulation system, therefore, there is a possibility that distortioncompensation data are largely increased.

In the technique shown in related art 3 and for improving theoutput-response characteristics with respect to an input control voltagein a power amplifier, the variable-output amplifier and the poweramplifier must be controlled simultaneously and adequately, a method ofadjusting and controlling a delay between control signals of the twoamplifiers is complicated, and a very rapid control is required in orderto correctly express amplitude signal components of a modulated signal.In the case where this technique is applied to the polar modulationsystem to realize linearization of the output of the power amplifierwith respect to the control voltage, therefore, a delay adjustingcircuit and a controlling circuit must be added, with the result thatthe circuit scale is greatly increased.

As described above, in any combination of related arts 1 to 3, whenlinearization of the output of the power amplifier with respect to thecontrol voltage is to be realized in the polar modulation system, it isimpossible to suppress increase of the circuit scale due to increase ofdistortion compensation data, or increase of the circuit scale due tothe addition of a delay adjusting circuit and a controlling circuit.

Furthermore, in any combination of related arts 1 to 3, when stable andrapid starting characteristics are to be acquired in a power amplifierwhich performs a burst operation, it is impossible to suppress increaseof the circuit scale due to the addition of a controlling circuit.

Next, in the technique for compensating AM-PM characteristics at asignal change point shown in related art 4, a system of feedbacking theoutput signal of the power amplifier 3000 is required, the delayingmeans 3307 is required, and therefore the circuit scale is increased. Inthe case where a transmitting apparatus is configured by using the phasecompensating apparatus shown in related art 4, the feedback system has aconfiguration in which the output signal of the power amplifier 3000branches from an interval between stages or the power amplifier 3000 andan antenna connected to the subsequent stage of the power amplifier3000. The feedback of the output signal of the power amplifier 3000increases a loss of an output portion of the power amplifier 3000.Therefore, the transmission efficiency of the transmitting apparatus islowered. In the case where the highest priority is given to thetransmission efficiency of the transmitting apparatus, consequently, thefeedback system in which the output signal of the power amplifier 3000branches off is not preferable.

Finally, in the technique for linearizing the output of a poweramplifier during a low-output power shown in related art 5, the meansfor controlling the amplitude of an input high-frequency signal of thepower amplifier includes a circuit which operates in the high-frequencyband, and hence there is a possibility that the control accuracy islowered.

The invention has been conducted in view of the above-discussed relatedcircumstances. It is an object of the invention to provide a distortioncompensating circuit in which, in the polar modulation system, whilesuppressing increase of compensation data and increase of the circuitscale, a modulated signal can be correctly expressed, or low-distortioncharacteristics of a power amplifier can be realized.

Means for Solving the Problems

First, the distortion compensating circuit of the invention is adistortion compensating circuit for compensating distortion of an outputsignal of an amplifier in a polar modulation system in which phasemodulation is performed based on a signal having at least a phasecomponent of a baseband quadrature signal, the phase-modulated signal isinput as an input high-frequency signal into the amplifier, andamplitude modulation corresponding to an amplitude component of thequadrature signal is synthesized by driving a control voltage of theamplifier, wherein the distortion compensating circuit comprises asteady characteristic compensating circuit which, based on output signalcharacteristics with respect to a control voltage value in a steadystate after an input of the control voltage, for each predeterminedinput high-frequency signal amplitude, linearizes the output signal ofthe amplifier in the steady state, and a transient characteristiccompensating circuit which adjusts the control voltage to compensatetransient response characteristics of the output signal during drivingof the control voltage.

According to the configuration, in the polar modulation system, responsecharacteristics of the output signal with respect to anamplitude-modulated signal input to the amplifier can be improved whilesuppressing increase of compensation data.

Second, the distortion compensating circuit of the invention is thefirst distortion compensating circuit wherein the steady characteristiccompensating circuit stores compensation data based on output signalamplitude characteristics with respect to the control voltage value, ina case where an unmodulated signal is input as an input high-frequencysignal into the amplifier.

According to the configuration, in addition to the effect of the firstdistortion compensating circuit, the compensation data can be easilyobtained.

Third, the distortion compensating circuit of the invention is thesecond distortion compensating circuit wherein the input high-frequencysignal is an unmodulated one-carrier signal, and the output signalamplitude characteristics are for a fundamental wave component of theinput high-frequency signal.

According to the configuration, in addition to the effects of the seconddistortion compensating circuit, the amount of the compensation data canbe further reduced.

Fourth, the distortion compensating circuit of the invention is any oneof the first to third distortion compensating circuits wherein thetransient characteristic compensating circuit has a first amplitudeinformation adjusting portion which performs the adjustment on thecontrol voltage after correction by the steady characteristiccompensating circuit.

According to the configuration, in addition to the effects of any one ofthe first to third distortion compensating circuits, the configurationcan be more simplified.

Fifth, the distortion compensating circuit of the invention is any oneof the first to third distortion compensating circuits wherein thetransient characteristic compensating circuit has a second amplitudeinformation adjusting portion which performs the adjustment on thecontrol voltage before correction by the steady characteristiccompensating circuit, to produce a control signal, and the steadycharacteristic compensating circuit refers the control signal which hasbeen adjusted by the transient characteristic compensating circuit, toread out the compensation data.

According to the configuration, in addition to the effects of any one ofthe first to third distortion compensating circuits, the configurationcan be more simplified.

Sixth, the distortion compensating circuit of the invention is thefourth or fifth distortion compensating circuit wherein the amplitudeinformation adjusting portion is a multiplying circuit which multipliesa first coefficient.

According to the configuration, in addition to the effects of the fourthor fifth distortion compensating circuit, the configuration can be moresimplified.

Seventh, the distortion compensating circuit of the invention is thesixth distortion compensating circuit wherein the multiplying circuitsets the first coefficient in accordance with step responsecharacteristics with respect to the control voltage of the amplifier.

According to the configuration, in addition to the effects of the sixthdistortion compensating circuit, the compensation accuracy can befurther improved.

Eighth, the distortion compensating circuit of the invention is theseventh distortion compensating circuit wherein, in a case where thestep response characteristics with respect to the control voltage of theamplifier are overshoot, the first coefficient is set so as to becompressed with respect to an input signal, and, in a case where thestep response characteristics are not overshoot, the first coefficientis set so as to be expanded with respect to the input signal.

According to the configuration, in addition to the effects of theseventh distortion compensating circuit, the compensation accuracy canbe further improved.

Ninth, the distortion compensating circuit of the invention is thefourth distortion compensating circuit wherein the steady characteristiccompensating circuit further stores compensation data which, in a casewhere an unmodulated one-carrier signal is input as an inputhigh-frequency signal into the amplifier, are based on passing phasecharacteristics of a fundamental wave component of the inputhigh-frequency signal with respect to the control voltage value, andrefers a control signal output from the first amplitude informationadjusting portion, to read out compensation data based on the passingphase characteristics for phase-correction of the phase component.

According to the configuration, in addition to the effects of the fourthdistortion compensating circuit, the compensation accuracy can befurther improved by correcting a phase-modulated signal in considerationof transient characteristics.

Tenth, the distortion compensating circuit of the invention is the fifthdistortion compensating circuit wherein the steady characteristiccompensating circuit further stores compensation data which, in a casewhere an unmodulated one-carrier signal is input as an inputhigh-frequency signal into the amplifier, are based on passing phasecharacteristics of a fundamental wave component of the inputhigh-frequency signal with respect to the control voltage value, andrefers the control signal after correction by the steady characteristiccompensating circuit, to read out compensation data based on the passingphase characteristics for phase-correction of the phase component.

According to the configuration, in addition to the effects of the fifthdistortion compensating circuit, the compensation accuracy can befurther improved by correcting a phase-modulated signal in considerationof transient characteristics.

Eleventh, the distortion compensating circuit of the invention is adistortion compensating circuit for compensating distortion of an outputsignal of an amplifier in a polar modulation system in which phasemodulation is performed based on a signal having at least a phasecomponent of a baseband quadrature signal, the phase-modulated signal isinput as an input high-frequency signal into the amplifier, andamplitude modulation corresponding to an amplitude component of thequadrature signal is synthesized by driving a control voltage of theamplifier, wherein the distortion compensating circuit comprises asteady characteristic compensating circuit which stores compensationdata based on passing phase characteristics with respect to a controlvoltage value in a steady state after an input of the control voltage,for each predetermined input high-frequency signal amplitude, andlinearizes the output signal of the amplifier in the steady state, and aphase compensating circuit which multiplies a reference signal forreading out the compensation data in the steady characteristiccompensating circuit by a second coefficient.

According to the configuration, AM-PM characteristics can be adjusted bya simple configuration.

Twelfth, the distortion compensating circuit of the invention is theeleventh distortion compensating circuit wherein the second coefficientis multiplied with reference to a reference signal which is maximumamong reference signals for reading out the compensation data in thesteady characteristic compensating circuit.

According to the configuration, in addition to the effect of theeleventh distortion compensating circuit, the compensation accuracy ofthe AM-PM characteristics can be further improved.

Thirteenth, the distortion compensating circuit of the invention is thetwelfth distortion compensating circuit wherein the distortioncompensating circuit further comprises an amplitude determining portionwhich calculates an instantaneous amplitude value of the control voltagesampled at constant intervals, the amplitude determining portion has afunction of setting a predetermined threshold based on the pluralinstantaneous amplitude values and determining increase or decrease of acontrol signal from a previous sampling timing, and, based on increaseor decrease of the control signal determined by the amplitudedetermining portion, the second coefficient which is to be set duringdecrease of the control signal is reduced with respect to the secondcoefficient which is to be set during increase of the control signal.

According to the configuration, in addition to the effects of thetwelfth distortion compensating circuit, it is possible to compensate achange of the AM-PM characteristics at a signal change point.

Fourteenth, the distortion compensating circuit of the invention is thetwelfth distortion compensating circuit wherein the phase compensatingcircuit switches over the second coefficient, thereby performingadjustment of synchronization between the phase component and theamplitude component.

According to the configuration, in addition to the effects of thetwelfth distortion compensating circuit, adjustment of synchronizationbetween the phase signal and the amplitude signal can be performed by asimple configuration.

Fifteenth, the distortion compensating circuit of the invention is anyone of the sixth to thirteenth distortion compensating circuits whereinthe distortion compensating circuit further comprises an amplitudedetermining portion which calculates an instantaneous amplitude value ofthe control voltage sampled at constant intervals, and switches over thefirst or second coefficient in accordance with the instantaneousamplitude value.

According to the configuration, in addition to the effects of any one ofthe sixth to thirteenth distortion compensating circuits, thecompensation accuracy can be further improved.

Sixteenth, the distortion compensating circuit of the invention is anyone of the sixth to thirteenth distortion compensating circuits whereinthe distortion compensating circuit further comprises an amplitudedetermining portion which calculates an instantaneous amplitude value ofthe control voltage sampled at constant intervals, the amplitudedetermining portion has a function of setting a predetermined thresholdbased on the plural instantaneous amplitude values and determiningincrease or decrease of the control signal from a previous samplingtiming, and the distortion compensating circuit sets the first or secondcoefficient in accordance with increase or decrease of the controlsignal determined by the amplitude determining portion.

According to the configuration, in addition to the effects of any one ofthe sixth to thirteenth distortion compensating circuits, thecompensation accuracy can be further improved.

Seventeenth, the distortion compensating circuit of the invention is anyone of the first to sixteenth distortion compensating circuits whereinthe information stored in the steady characteristic compensating circuitis an approximation polynomial of an output signal amplitude or passingphase characteristics with respect to the control voltage value in thesteady state after input of the control voltage, in a predeterminedinput high-frequency signal amplitude.

According to the configuration, in addition to the effects of any one ofthe first to sixteenth distortion compensating circuits, the amount ofthe compensation data can be further reduced.

Eighteenth, the distortion compensating circuit of the invention is adistortion compensating circuit for compensating distortion of an outputsignal of an amplifier in a polar modulation system in which phasemodulation is performed based on a signal having at least a phasecomponent of a baseband quadrature signal, the phase-modulated signal isinput as an input high-frequency signal into the amplifier, andamplitude modulation corresponding to an amplitude component of thequadrature signal is synthesized by driving a control voltage of theamplifier, wherein the distortion compensating circuit further comprisesan amplitude adjusting portion which multiplies the signal having atleast the phase component of the baseband quadrature signal, by a thirdcoefficient, and adjusts an amplitude of the signal.

According to the configuration, the accuracy of the compensation of thephase-modulated signal can be further improved by adjusting theamplitude of the input high-frequency signal of the amplifier.

Nineteenth, the distortion compensating circuit of the invention is anyone of the sixth to eighteenth distortion compensating circuits whereinthe distortion compensating circuit switches over the first, second, orthird coefficient in accordance with a transmission output power.

According to the configuration, in addition to the effects of any one ofthe sixth to eighteenth distortion compensating circuits, an adequatecoefficient according to the transmission power can be selected, and thecompensation accuracy can be further improved.

Twentieth, the distortion compensating circuit of the invention is theeighteenth distortion compensating circuit wherein the distortioncompensating circuit further comprises a variable-band low-pass filter,and, in accordance with the transmission output power, switches over thethird coefficient and a band of the low-pass filter.

According to the configuration, in addition to the effects of theeighteenth distortion compensating circuit, noises in an output of theamplifier can be reduced.

Twenty-first, the distortion compensating circuit of the invention isthe twentieth distortion compensating circuit wherein the distortioncompensating circuit further comprises a steady characteristiccompensating circuit which stores compensation data based on passingphase characteristics with respect to a control voltage value in asteady state after an input of the control voltage, for eachpredetermined input high-frequency signal amplitude, and whichlinearizes the output signal of the amplifier in the steady state, and aphase compensating circuit which multiplies a reference signal forreading out the compensation data in the steady characteristiccompensating circuit, by a second coefficient, and the phasecompensating circuit multiplies the second coefficient with reference toa reference signal which is maximum among reference signals for readingout the compensation data in the steady characteristic compensatingcircuit, and switches over the second coefficient in accordance with theswitching of the band of the low-pass filter, thereby performingadjustment of synchronization between the phase component and theamplitude component.

According to the configuration, in addition to the effects of thetwentieth distortion compensating circuit, a loss of synchronizationbetween the amplitude signal and the phase signal due to switching ofthe band of the low-pass filter can be compensated by a simpleconfiguration.

Twenty-second, the distortion compensating circuit of the invention isany one of the sixth, eleventh, twelfth, or eighteenth distortioncompensating circuit wherein the distortion compensating circuitswitches over the first, second, or third coefficient on the basis of adetection signal which is obtained by detecting an environmentaltemperature, thereby compensating temperature characteristics of theoutput signal.

According to the configuration, in addition to the effects of any one ofthe eleventh, twelfth, or eighteenth distortion compensating circuit,even when the environmental temperature varies, response characteristicsof the output signal of the amplifier can be improved while suppressingincrease of the compensation data.

Twenty-third, the distortion compensating circuit of the invention isany one of the sixth, eleventh, twelfth, or eighteenth distortioncompensating circuit wherein the distortion compensating circuitswitches over the first, second, or third coefficient in accordance witha frequency input into the amplifier, thereby compensating frequencycharacteristics of the output amplitude.

According to the configuration, in addition to the effects of any one ofthe eleventh, twelfth, or eighteenth distortion compensating circuit,even when a change occurs in the transmission frequency, responsecharacteristics of the output signal of the amplifier can be improvedwhile suppressing increase of the compensation data.

First, the transient characteristic compensating circuit of theinvention is a transient characteristic compensating circuit forspeeding up starting characteristics of a transistor circuit whichcontrols an output signal amplitude by adjusting a control voltage,wherein the transient characteristic compensating circuit is amultiplying circuit which multiplies the control voltage by a fourthcoefficient, and the multiplying circuit sets the fourth coefficient inaccordance with step response characteristics with respect to thecontrol voltage of the amplifier.

According to the configuration, the starting characteristics of thetransistor circuit are speeded up by a simple configuration.

Second, the transient characteristic compensating circuit of theinvention is the first transient characteristic compensating circuitwherein, in a case where the step response characteristics are notovershoot, the fourth coefficient is set so as to be expanded withrespect to the input signal.

According to the configuration, in addition to the effect of the firsttransient characteristic compensating circuit, the startingcharacteristics of the transistor circuit are speeded up by a simplerconfiguration.

The ramp controlling circuit comprises the first or second transientcharacteristic compensating circuit.

According to the configuration, it is possible to realize a rampcontrolling circuit in which the starting characteristics of thetransistor circuit are speeded up by a simple configuration.

The radio communication apparatus of the invention comprises any one ofthe first to twenty-third distortion compensating circuits, the first orsecond transient characteristic compensating circuit, or the rampcontrolling circuit.

According to the configuration, it is possible to realize a highlyefficient low-distortion transmitting apparatus.

EFFECTS OF THE INVENTION

According to the invention, a distortion compensating circuit can beprovided in which, in the polar modulation system, while suppressingincrease of compensation data and increase of the circuit scale, amodulated signal can be correctly expressed, or low-distortioncharacteristics of a power amplifier can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS

[FIG. 1] A view showing an example of a schematic configuration of apolar modulating circuit of a first embodiment of the invention.

[FIG. 2] A view showing another example of the schematic configurationof the polar modulating circuit of the first embodiment of theinvention.

[FIG. 3] A view showing a further example of the schematic configurationof the polar modulating circuit of the first embodiment of theinvention.

[FIG. 4] A view showing step response characteristics of an outputamplitude with respect to a control voltage in a state where an inputhigh-frequency signal having a level at which a power amplifier operatesin saturation is given.

[FIG. 5] A frequency spectrum of a power amplifier output in a casewhere the first embodiment is applied to the polar modulation systemusing an 8-PSK modulated wave.

[FIG. 6] A view showing an example of a schematic configuration of apolar modulating circuit of a second embodiment of the invention.

[FIG. 7] A view showing another example of the schematic configurationof the polar modulating circuit of the second embodiment of theinvention.

[FIG. 8 a] A view showing an example of a schematic configuration of apolar modulating circuit of a third embodiment of the invention.

[FIG. 8 b] A view showing another example of the schematic configurationof the polar modulating circuit of the third embodiment of theinvention.

[FIG. 9] A view showing AM-AM characteristics of a power amplifier.

[FIG. 10] A view showing a further example of the schematicconfiguration of the polar modulating circuit of the third embodiment ofthe invention.

[FIG. 11] A view showing an example of a schematic configuration of apolar modulating circuit of a fourth embodiment of the invention.

[FIG. 12] A view showing another example of the schematic configurationof the polar modulating circuit of the fourth embodiment of theinvention.

[FIG. 13] A view showing passing phase characteristics of a poweramplifier with respect to a control voltage (steady state).

[FIG. 14] A view showing an example of a schematic configuration of apolar modulating circuit of a fifth embodiment of the invention.

[FIG. 15] A view showing another example of the schematic configurationof the polar modulating circuit of the fifth embodiment of theinvention.

[FIG. 16] A view showing an example of a schematic configuration of apolar modulating circuit of a sixth embodiment of the invention.

[FIG. 17] A view showing another example of the schematic configurationof the polar modulating circuit of the sixth embodiment of theinvention.

[FIG. 18] A view showing a further example of the schematicconfiguration of the polar modulating circuit of the sixth embodiment ofthe invention.

[FIG. 19] A view showing an example of a schematic configuration of apolar modulating circuit of a seventh embodiment of the invention.

[FIG. 20] A view showing another example of the schematic configurationof the polar modulating circuit of the seventh embodiment of theinvention.

[FIG. 21] A view showing a further example of the schematicconfiguration of the polar modulating circuit of the seventh embodimentof the invention.

[FIG. 22] A view showing an example of a schematic configuration of apolar modulating circuit of an eighth embodiment of the invention.

[FIG. 23] A view showing another example of the schematic configurationof the polar modulating circuit of the eighth embodiment of theinvention.

[FIG. 24] A view showing a further example of the schematicconfiguration of the polar modulating circuit of the eighth embodimentof the invention.

[FIG. 25] A view showing a schematic configuration of a polar modulatingcircuit of a ninth embodiment of the invention.

[FIG. 26] A view showing an amplitude signal during 8-PSK modulation.

[FIG. 27] A view showing passing phase characteristics in a case where acontrol voltage which is gradually changed (monotonically increased ordecreased) with respect to the elapse of time is applied to a poweramplifier.

[FIG. 28] A view showing a transmission power regulation for a mobilestation.

[FIG. 29] A view showing an output amplitude and passing phasecharacteristics with respect to an input high-frequency signal amplitudeof a power amplifier (a control voltage is in a steady state).

[FIG. 30] A block diagram showing a related predistortion system.

[FIG. 31] A block diagram showing a related polar modulation system towhich predistortion type distortion compensation is applied.

[FIG. 32] A view showing output signal amplitude characteristics of apower amplifier with respect to a control voltage.

[FIG. 33] A block diagram showing means for improving output-responsecharacteristics with respect to the control voltage in a related poweramplifier, and low-output linearizing means in the related poweramplifier.

[FIG. 34] A block diagram showing a related apparatus forphase-compensating at a signal change point.

[FIG. 35] A view showing passing phase characteristics of a poweramplifier with respect to a control voltage (steady state).

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS

-   1 polar coordinate converting means-   2 amplitude modulating means-   3 phase modulating means-   4 power amplifier-   5, 5 b orthogonal coordinate converting means-   6 quadrature modulating means-   10, 20, 30, 40, 50, 60, 70, 80, 90 distortion compensating circuit-   11, 11 b, 11 c, 11 d steady characteristic compensating circuit-   12 amplitude information correcting means-   13 first amplitude information adjusting portion-   14, 34 transient characteristic compensating circuit-   15 first coefficient selecting portion-   16 amplitude determining portion-   17 phase information correcting means-   33 second amplitude information adjusting portion-   35 second coefficient selecting portion-   43 third amplitude information adjusting portion-   44 phase compensating circuit-   45 third coefficient selecting portion-   53 fourth amplitude information adjusting portion-   54 transient characteristic/phase compensating circuit-   55 fourth coefficient selecting portion-   71 multiplying circuit-   81 amplitude adjusting portion-   82 fifth coefficient selecting portion-   53 b fifth amplitude information adjusting portion-   55 b sixth coefficient selecting portion-   91 low-pass filter-   92 band selecting portion

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

A first embodiment of the invention describes a method which has notbeen solved by any combination of related arts 1 to 3, and which, in thepolar modulation system, realizes linearization of an output of a poweramplifier with respect to a control voltage without producing increaseof the circuit scale due to increase of distortion compensation data.

As another technique for realizing linearization of an output of a poweramplifier with respect to a control voltage, there is a method whichperforms a process of comparing transmission data with demodulated dataof an output signal from a power amplifier, and updating compensationdata so as to reduce an error (hereinafter, referred to as adaptiveprocess). A method will be described which realizes linearization of anoutput of a power amplifier with respect to a control voltage withoutusing a feedback system in order to avoid lowering of the transmissionefficiency of a transmitting apparatus caused by a branching portion foran output signal of the power amplifier that is required in theconfiguration a circuit for performing the adaptive process.

FIG. 1 is a view showing an example of a schematic configuration of apolar modulating circuit of the first embodiment of the invention.

As shown in FIG. 1, the polar modulating circuit of the first embodimentof the invention comprises polar coordinate converting means 1, adistortion compensating circuit 10, amplitude modulating means 2, phasemodulating means 3, a power amplifier 4, and orthogonal coordinateconverting means 5.

In the case where the polar modulating circuit of the invention is usedin a transmitting apparatus, the polar coordinate converting means 1separates an orthogonal coordinate signal (IQ signal) input from abaseband signal generating portion of the transmitting apparatus whichis not shown, into amplitude information r(t) and phase information θ(t)having a constant amplitude. The polar coordinate converting means 1normalizes r(t) so that the maximum value is 1.

The distortion compensating circuit 10 performs a predetermineddistortion compensating process on the amplitude information r(t) andthe phase information θ(t). The detailed operation of the distortioncompensating circuit 10 will be described later.

The amplitude modulating means 2 drives a control voltage of the poweramplifier 4 on the basis of the amplitude information output from thedistortion compensating circuit 10.

In the case where the polar modulating circuit of the invention is usedin a transmitting apparatus, the orthogonal coordinate converting means5 converts the phase information output from the distortion compensatingcircuit 10 to an IQ signal (I11(t), Q11(t)) having a constant amplitudeon the basis of output amplitude information S2 transmitted from acontrolling portion of the transmitting apparatus which is not shown.That is, the output amplitude information S2 determines the amplitudevalue of the constant-amplitude IQ signal. The output amplitudeinformation S2 is set to a value at which the phase modulating means 3is not saturated, and may be stored in the orthogonal coordinateconverting means 5 instead of being transmitted from the controllingportion of the transmitting apparatus. For example, the output amplitudeinformation S2 may be set to 1, and an attenuating circuit may bedisposed in an IQ signal inputting portion of the phase modulating means3 so that the phase modulating means 3 is not saturated.

The phase modulating means 3 performs phase modulation on the basis ofthe IQ signal (I11(t), Q11(t)) output from the orthogonal coordinateconverting means 5. The phase modulating means 3 may include also phasemodulating means which is configured so as to have quadrature modulatingmeans, and which is called an offset PLL system. The phase modulatingmeans 3 may include phase modulating means which is configured so as tohave a fractional frequency divider, and which is called a fractional-NPLL system. In case of the fractional-N PLL system, the phase modulatingmeans 3 performs phase modulation on the basis of the phase informationθ output from the distortion compensating circuit 10 instead of the IQsignal (I11(t), Q11(t)) output from the orthogonal coordinate convertingmeans 5.

The power amplifier 4 synthesizes amplitude modulation on aphase-modulated signal output from the phase modulating means 3, on thebasis of an output signal of the amplitude modulating means 2 serving asa control signal.

Another example of the polar modulating circuit of the first embodimentof the invention may comprise the configuration shown in FIG. 2.

FIG. 2 is a view showing another example of the schematic configurationof the polar modulating circuit of the first embodiment of theinvention. In the polar modulating circuit of this example, quadraturemodulating means 6 and orthogonal coordinate converting means 5 b aredisposed in place of the phase modulating means 3 and the orthogonalcoordinate converting means 5.

The orthogonal coordinate converting means 5 b synthesizes the amplitudeinformation r(t) output from the polar coordinate converting means 1with the phase information output from the distortion compensatingcircuit 10, to output an IQ signal (I12(t), Q12(t)).

The quadrature modulating means 6 performs quadrature modulation basedon the IQ signal (I12(t), Q12(t)) output from the orthogonal coordinateconverting means 5. A high-frequency signal having an amplitudecomponent which is quadrature-modulated by the quadrature modulatingmeans 6 becomes as an input signal of the power amplifier 4. Anattenuating circuit may be disposed in an IQ signal inputting portion ofthe quadrature modulating means 6 so that the quadrature modulatingmeans 6 is not saturated.

Next, the distortion compensating circuit 10 will be described indetail. As shown in FIGS. 1 and 2, the distortion compensating circuit10 has a steady characteristic compensating circuit 11, amplitudeinformation correcting means 12, a transient characteristic compensatingcircuit 14 having a first amplitude information adjusting portion 13, afirst coefficient selecting portion 15, an amplitude determining portion16, and phase information correcting means 17.

Transmission level information S1 is transmission level information ofthe power amplifier 4 which, in the case where the polar modulatingcircuit of the invention is used in a transmitting apparatus, istransmitted from a controlling portion of the transmitting apparatuswhich is not shown. The information is input into the steadycharacteristic compensating circuit 11 and the first coefficientselecting portion 15. For the transmission level information S1,specifically, the case where the polar modulating circuit of theinvention is applied to a mobile station transmitting apparatus whichperforms transmission in 8-PSK modulation in the 900 MHz GSM band willbe described. At the output end of an antenna which is connected to arear stage of the power amplifier 4, and which is not shown, theinformation is defined between 33 dBm and 5 dBm in steps of 2 dB.Namely, the transmission level information S1 is determined on the basisof the transmission power regulation in uplink for a mobile stationtransmitting apparatus such as shown in FIG. 28.

For output signal amplitude characteristics and passing phasecharacteristics of a fundamental wave component from the power amplifier4, the steady characteristic compensating circuit 11 stores, as theAM-AM characteristics, data in the absolute value format of the controlvoltage with respect to the output signal amplitude, or a predeterminedvalue (data in the format of a difference value) which, after the inputcontrol signal amplitude is multiplied or divided by the above-mentionedpredetermined value, is normalized with the input control signal so asto attain the absolute value, and stores in the memory passing phasecharacteristic data with respect to the control voltage as the AM-PMcharacteristics.

The output signal amplitude characteristics and passing phasecharacteristics of a fundamental wave component from the power amplifier4 are characteristics that are acquired in the case where an unmodulatedone-carrier which can be obtained by using a network analyzer and thelike, and which has a predetermined level (constant value) is input as ahigh-frequency input signal to the power amplifier 4.

The AM-AM and AM-PM characteristics are characteristics which, duringthe acquisition time of the output signal amplitude characteristics andthe passing phase characteristics, are acquired at each switching of thecontrol voltage that is set to the constant value (hereinafter, referredto as steady control voltage).

The relationships of input and output signals in the steadycharacteristic compensating circuit 11 respectively output an amplitudecorrection signal S11 and a phase correction signal S12 while, asaddress designation signals, using the input amplitude information r(t)and an output signal r11(t) from the amplitude information correctingmeans 12. The steady characteristic compensating circuit 11 performs aprocess of normalizing the AM-AM characteristics based on thetransmission level information S1. Specifically, based on the maximumtransmission power in which the maximum value—the average value (peakfactor) of amplitude information corresponding to the modulation systemis considered, normalization of an output signal amplitude in storedAM-AM data is executed on a desired output level (average power),whereby correction is performed for each desired output level. As aresult of the normalization, access to AM-AM data with using the inputamplitude information r(t) as an address designation signal is enabled.

Such a circuit is referred to as a steady characteristic compensatingcircuit, in order to show that, because the stored AM-AM and AM-PMcharacteristics are characteristics at a timing when the characteristicssettle into a steady state after the control voltage is input, i.e.,characteristics with respect to the steady control voltage,characteristic compensation which is executed based on thecharacteristics is for steady characteristics.

The amplitude information correcting means 12 performs correction on theamplitude information r(t) output from the polar coordinate convertingmeans 1, on the basis of the amplitude correction signal S11 output fromthe steady characteristic compensating circuit 11.

The first amplitude information adjusting portion 13 multiplies theamplitude information r11(t) output from the amplitude informationcorrecting means 12 by predetermined coefficient information (func1) tooutput amplitude information r12(t).

The first coefficient selecting portion 15 stores a table of coefficientinformation corresponding to the transmission level information S1, inorder to set the coefficient information (func1) of the first amplitudeinformation adjusting portion 13.

The amplitude determining portion 16 has a function of calculating aninstantaneous amplitude value (|r(t)|) of the amplitude information r(t)sampled at constant intervals, and a function of setting a predeterminedthreshold based on plural instantaneous amplitude values and determiningincrease or decrease (Δr(t)) of the amplitude value of the amplitudeinformation r(t) from a previous sampling timing, thereby calculating asignal change point.

The phase information correcting means 17 performs correction on thephase information θ(t) on the basis of the phase correction signal S12output from the steady characteristic compensating circuit 11.

A further example of the polar modulating circuit of the firstembodiment of the invention may comprise the configuration shown in FIG.3.

FIG. 3 is a view showing the further example of the schematicconfiguration of the polar modulating circuit of the first embodiment ofthe invention. The polar modulating circuit of this example isconfigured so that the orthogonal coordinate converting means 5 b andthe phase information correcting means 17 are removed away from thepolar modulating circuit of FIG. 2, and the input IQ signal of thequadrature modulating means 6 are changed from I12(t), Q12(t) to an IQsignal (I(t), Q(t)) input from the baseband signal generating portion ofthe transmitting apparatus which is not shown, thereby omitting thephase correction of the phase-modulated signal.

In the case where the polar modulating circuit of the invention is usedin a transmitting apparatus, a digital-analog converting circuit(hereinafter, abbreviated to DA converter) which is not shown is placedbetween, in FIG. 1, stages of the first amplitude information adjustingportion 13 and the amplitude modulating means 2, and stages of theorthogonal coordinate converting means 5 and the phase modulating means3, between, in FIG. 2, stages of the first amplitude informationadjusting portion 13 and the amplitude modulating means 2, and stages ofthe orthogonal coordinate converting means 5 b and the quadraturemodulating means 6, and between, in FIG. 3, stages between the firstamplitude information adjusting portion 13 and the amplitude modulatingmeans 2, and in front of the quadrature modulating means 6.

Next, the operation of the distortion compensating circuit 10 of thefirst embodiment of the invention will be described. First, prior to thedescription of the operation of the distortion compensating circuit,step response characteristics with respect to the control voltage of thepower amplifier will be described.

FIG. 4 is a view showing step response characteristics of an outputsignal amplitude with respect to a control voltage in a state where aninput high-frequency signal amplitude having a level at which a poweramplifier operates in saturation is given. In FIG. 4, the abscissaindicates the time elapsed after inputting of the control signal intothe power amplifier, and the ordinate indicates the amplitude of theoutput signal of the power amplifier.

As shown in FIG. 4, when the control voltage supplied to the poweramplifier is changed from 0 v to a predetermined level (step response),in a state where an input high-frequency signal having a level at whichthe power amplifier operates in saturation is given, transient responsecharacteristics are exhibited before a steady state where the outputamplitude is stabilized is attained. In the example of FIG. 4, stepresponse characteristics with respect to two different control voltagevalues (steady control voltage values) are shown, and the outputamplitudes from the power amplifier in steady characteristics aredifferent. The amplitude of the input high-frequency signal duringacquisition of the step response characteristics is at a level at whichthe power amplifier operates in saturation, and a constant value. In thetwo step response characteristics shown in FIG. 4, the steady controlvoltage value of the higher output amplitude is higher than that of thelower output amplitude.

Next, a method and procedure of feeding back an error of theabove-mentioned transient response portion from a predetermined levelafter the output signal from the power amplifier 4 is branched, andcorrecting the error without performing the adaptive process will bedescribed.

The data (AM-AM characteristics, AM-PM characteristics) stored in thesteady characteristic compensating circuit 11 are anti-control voltage(steady state) characteristics of the output signal amplitude andpassing phase rotation amount of the power amplifier 4 which can beacquired by using a network analyzer while giving the priority toeasiness of data acquisition, and switching over plural steady controlvoltage values that have a constant value during data acquisition. Whendistortion compensation is executed with referring the data which arecharacteristics in the steady state, a desired output amplitude cannotbe expressed by the output signal r11(t) from the amplitude informationcorrecting means 12 because of influence of the transient response shownin FIG. 4.

Therefore, step response characteristics of the power amplifier 4 duringsupply of a control voltage having a constant value at which the averageoutput level of a modulated signal becomes a desired level arepreviously measured for each transmission output power defined in astandard of a radio system (for example, the GSM standard which has beendescribed as an example in the paragraph of the background art). In thecase where transient response characteristics in the step responsecharacteristics are in an overshoot state as in the high outputamplitude in FIG. 4, the first coefficient selecting portion 15 outputsthe coefficient information (func1) indicated by Expression (2) to thefirst amplitude information adjusting portion 13 so that r11(t) andr12(t) have the relationship indicated by Expression (1).r11(t)>r12(t)  (1)func1<1  (2)

By contrast, in the case where the response converges without exceedinga predetermined value during the transient response period as in the lowoutput amplitude in FIG. 4, the first coefficient selecting portion 15outputs the coefficient information (func1) indicated by Expression (4)to the first amplitude information adjusting portion 13 so that r11(t)and r12(t) have the relationship indicated by Expression (3).r11(t)≦r12(t)  (3)func1≧1  (4)

Namely, in the case where a control voltage having a constant value atwhich the average output amplitude in the transmission modulated signalis obtained is given, when the starting characteristics of the poweramplifier 4 are overshoot, the amplitude information r11(t) on whichcorrection has been executed by the steady characteristics iscompressed, and, in case of the inverse characteristics, r11(t) isexpanded, whereby a desired output amplitude can be obtained inconsideration of the transient response.

In the GSM system, for example, a period when a modulated signal is nottransmitted exists between time slots, it is required that a poweramplifier is activated with the start of one time slot period, andstopped with the end of the one time slot period, and the transmissionoutput power in one time slot is constant. When the distortioncompensating circuit of the first embodiment of the invention is appliedto the GSM system, therefore, coefficient information can be output onthe basis of the transmission level information S1 for each time slot.

In this way, in the distortion compensating circuit of the firstembodiment of the invention, distortion compensation in consideration ofinfluence of the transient response can be performed simply by addingthe first coefficient selecting portion 15 storing the table of thecoefficient information (func1) corresponding to the transmission levelinformation S1, and the transient characteristic compensating circuit 14which multiplies the coefficient information (func1), to a related polarmodulating circuit.

Namely, enormous compensation data in the time axis, a control circuitfor performing a complex control, and a delay adjusting circuit whichare necessary in the case where transient response characteristics areto be compensated based on related arts 1 to 3 are not required, and thecircuit scale can be reduced.

FIG. 5 shows a frequency spectrum of a power amplifier output in thecase where the first embodiment of the invention is applied to the polarmodulation system using an 8-PSK modulated wave. In FIG. 5, the abscissaindicates the frequency, and the ordinate indicates the power level.When the distortion compensating circuit of the first embodiment of theinvention is used, it is possible to realize the spectrum shown in FIG.5.

As described referring to FIG. 4, transient response characteristics aredifferent in accordance with the absolute value of the output amplitudeof the power amplifier 4. Therefore, not only in the case where thetransmission output power (average power) is controlled based on thetransmission level information S1, but also under conditions that thesame output power is set, there is a possibility that the transientresponse characteristics are different depending on the absolute valueof the amplitude of the output signal from the amplitude modulatingmeans 2.

Therefore, it is preferable to have a configuration where step responsecharacteristics of the power amplifier 4 in the case where the steadycontrol voltage level is set more finely than a set value of the steadycontrol voltage satisfying the transmission output power regulation arepreviously measured, and the first coefficient selecting portion 15prepares a table corresponding to an input signal (|r(t)|), and switchesover the coefficient information (func1) which is output in accordancewith the input signal.

In the first embodiment of the invention, the method of, in order toavoid lowering of the transmission efficiency of a transmittingapparatus, realizing linearization of the output of the power amplifier4 with respect to a change of the control voltage without branching theoutput signal from the power amplifier 4 has been described.

In the case where lowering of the transmission efficiency of thetransmitting apparatus is allowed, or where a circuit for branching theoutput signal from the power amplifier 4 is already connected to thepolar modulating circuit, however, the same effects can be attained alsoin a configuration where a table corresponding to the transmission levelinformation S1 is not disposed, and the coefficient information (func1)is adequately switched over while an adjacent-channel leakage power ofthe output spectrum of the power amplifier 4 is directly monitored bymeans which is not shown, or a baseband signal after demodulation of thespectrum is monitored, or so as to minimize an error between thebaseband signal and the transmission data.

Also in the cases where the frequency of the input high-frequency signalof the power amplifier 4 is different, and where the environmentaltemperature is changed, there is a possibility that the transientresponse characteristics are different. In the case where the polarmodulating circuit of the invention is used in a transmitting apparatus,therefore, it is further preferable to have a configuration where atable corresponding to the transmission frequency and the environmentaltemperature is prepared in the first coefficient selecting portion 15,and the output coefficient information (func1) is switched over inaccordance with transmission frequency information transmitted from thecontrolling portion of the transmitting apparatus which is not shown,temperature information from a temperature sensor which is not shown, orconsumption current information from a circuit which monitors, forexample, the consumption current (the collector current and the like) ofthe power amplifier that is equivalent to the temperature information.

In the case where lowering of the transmission efficiency of thetransmitting apparatus is allowed, or where a circuit for branching theoutput signal from the power amplifier 4 is already connected to thepolar modulating circuit, the same effects can be attained also in aconfiguration where the table corresponding to the transmissionfrequency and the environmental temperature, and the temperature sensorare not disposed, and the coefficient information (func1) is adequatelyswitched over while an adjacent-channel leakage power of the outputspectrum of the power amplifier 4 is directly monitored by means whichis not shown, or a baseband signal after demodulation of the spectrum ismonitored, or so as to minimize an error between the baseband signal andthe transmission data.

As described above, in the distortion compensating circuit of the firstembodiment of the invention, relating to distortion compensation usingthe AM-AM and AM-PM characteristics in steady characteristics to bestored in the steady characteristic compensating circuit 11, amplitudeinformation after amplitude correction is multiplied with thecoefficient information (func1) expressing the transient response. Inthe polar modulation system, while suppressing increase of compensationdata, therefore, amplitude information relating to a modulated signalcan be correctly expressed, or namely low-distortion characteristics ofthe power amplifier can be realized.

In the first embodiment of the invention, the case where a networkanalyzer is used has been described as the method of acquiring datawhich are origins of the data to be stored in the steady characteristiccompensating circuit 11. However, it is a matter of course thatcharacteristics of the power amplifier 4 may be acquired by othermeasuring means.

It is supposed that the steady characteristic compensating circuit 11stores the AM-AM and AM-PM characteristics as table data. Alternatively,polynomial approximation may be conducted based on the acquired data,and, with respect to the input terminal, a correction signal may beoutput based on the approximation function.

In the first embodiment of the invention above, the effect thatamplitude information relating to a modulated signal in datatransmission is correctly expressed has been described. Alternatively,the coefficient information (func1) expressing the transient responsemay be adjusted with respect to a time elapsed from the starting, sothat it is possible to obtain another effect that startingcharacteristics (ramp control) of a power amplifier which performs aburst operation is speeded up while ensuring stability.

Specifically, in the case where, although rapid starting characteristicsare requested, the response converges without exceeding a predeterminedvalue during the transient response period as in the low outputamplitude in FIG. 4, the coefficient information (func1) indicated byExpression (5) is output to the first amplitude information adjustingportion 13 based on step response characteristics with respect to thecontrol voltage which are previously acquired, in an early stage ofstarting (0 to t1), so that a control voltage that is higher than acontrol voltage at which a predetermined level is obtained is applied tothe amplifier. In the subsequent period (after t1), the coefficientinformation (func1) indicated by Expression (6) is output to the firstamplitude information adjusting portion 13. For example, the coefficientinformation (func1) can be set in correspondence with the transmissionlevel information S1 indicative of the output amplitude of theamplifier.

In this way, the level adjustment of the control voltage using thecoefficient information (func1) is executed for the time elapsed fromthe starting, whereby the starting characteristics of the poweramplifier can be speeded up. Furthermore, a circuit for feeding back theoutput signal of the amplifier is not required. Therefore, oscillationdue to addition of a feedback circuit can be avoided, and also stabilityis ensured.func1>1  (5)func1=1  (6)

Therefore, a ramp controlling circuit for a power amplifier may beconfigured by using the distortion compensating circuit of the firstembodiment of the invention.

In order to conduct high-speed communication, for example, a cellularsystem such as the GSM, a wireless LAN system such as IEEE 802.11a/b/g,or the UWB (Ultra Wide Band), the circuit can be applied to a system inwhich rapid starting characteristics for a pulse signal are requested.

In the above, starting characteristics of a power amplifier have beendescribed. It is a matter of course that, even when the circuit isapplied to an amplifier located in a front stage of a power amplifier,or an oscillator, the effect that starting characteristics is speeded upis similarly attained.

Second Embodiment

A second embodiment of the invention describes a method which has beendescribed in the first embodiment of the invention, and in which, in thepolar modulation system, while suppressing increase of compensationdata, amplitude/phase information relating to a modulated signal iscorrectly expressed by performing phase compensation based on a signalto which transient characteristic compensation is reflected.

FIG. 6 is a view showing an example of a schematic configuration of apolar modulating circuit of the second embodiment of the invention, andFIG. 7 is a view showing another example of the schematic configurationof the polar modulating circuit of the second embodiment of theinvention. The portions which are duplicated with those of the polarmodulating circuit of FIG. 1 or 2 which has been described in the firstembodiment of the invention are denoted by the same reference numerals.

As shown in FIGS. 6 and 7, in a distortion compensating circuit 20 ofthe second embodiment of the invention, the steady characteristiccompensating circuit 11 stores in the memory the AM-AM and AM-PMcharacteristics in the same data format as the first embodiment of theinvention, and outputs a phase correction signal S22 while setting theoutput signal r12(t) from the first amplitude information adjustingportion 13 as an address designation signal. The method of producing theamplitude correction signal S11 is identical with the first embodimentof the invention, and its description is omitted.

The phase information correcting means 17 performs correction on thephase information θ(t) on the basis of the phase correction signal S22output from the steady characteristic compensating circuit 11, andoutputs phase information θ2(t) after correction to the orthogonalcoordinate converting means 5 or the orthogonal coordinate convertingmeans 5 b.

In the same operation as the first embodiment of the invention, theorthogonal coordinate converting means 5 of FIG. 6 outputs I21(t) andQ21(t) to the phase modulating means 3.

In the same operation as the first embodiment of the invention, theorthogonal coordinate converting means 5 b of FIG. 7 outputs I22(t) andQ22(t) to the quadrature modulating means 6.

Namely, as compared with the distortion compensating circuit 10 shown inFIGS. 1 and 2, the distortion compensating circuit is different in that,when accessing AM-PM data, the steady characteristic compensatingcircuit 11 of the distortion compensating circuit 10 sets r11(t) as theaddress designation signal, and by contrast the steady characteristiccompensating circuit 11 of the distortion compensating circuit 20 setsr12(t) as an address designation signal.

In the case where the polar modulating circuit of the invention is usedin a transmitting apparatus, a DA converter which is not shown is placedbetween, in FIG. 6, stages of the first amplitude information adjustingportion 13 and the amplitude modulating means 2, and stages of theorthogonal coordinate converting means 5 and the phase modulating means3, and between, in FIG. 7, stages of the first amplitude informationadjusting portion 13 and the amplitude modulating means 2, and stagesbetween the orthogonal coordinate converting means 5 b and thequadrature modulating means 6.

According to the configuration, when the address designation signal inthe case where the AM-PM data stored in the steady characteristiccompensating circuit 11 are to be accessed is set to the amplitudeinformation r12(t) in which transient response characteristics of theoutput signal when the control voltage fluctuates are considered, it ispossible to consider transient response characteristics during controlvoltage fluctuation, also in phase correction data.

As described above, in the distortion compensating circuit of the secondembodiment of the invention, relating to distortion compensation usingthe AM-AM and AM-PM characteristics in steady characteristics to bestored in the steady characteristic compensating circuit 11, a signalwhich is obtained by multiplying amplitude information after amplitudecorrection by the coefficient information (func1) expressing thetransient response is set as the address designation signal when thephase correction signal is to produced. In the polar modulation system,while suppressing increase of compensation data, therefore,amplitude/phase information relating to a modulated signal can becorrectly expressed, or namely low-distortion characteristics of thepower amplifier can be realized.

Third Embodiment

A third embodiment of the invention describes a method different fromthe first embodiment of the invention, relating to a method which, inthe polar modulation system, realizes linearization of an output of apower amplifier with respect to a control voltage without using afeedback system, in order to avoid lowering of the transmissionefficiency of a transmitting apparatus caused by a branching portion foran output signal of the power amplifier that is required in theconfiguration a circuit for performing a process of comparingtransmission data with demodulated data of an output signal from thepower amplifier, and updating compensation data so as to reduce an error(hereinafter, referred to as adaptive process).

Furthermore, the embodiment describes a method of easily adjusting theinclination of the AM-AM characteristics of the power amplifier in orderto compensate frequency and temperature characteristics of the poweramplifier, and the like.

FIG. 8( a) is a view showing an example of a schematic configuration ofa polar modulating circuit of the third embodiment of the invention, andFIG. 8( b) is a view showing another example of the schematicconfiguration of the polar modulating circuit of the third embodiment ofthe invention. The portions which are duplicated with those of the polarmodulating circuit of FIG. 1 or 2 which has been described in the firstembodiment of the invention are denoted by the same reference numerals.

As shown in FIGS. 8( a) and 8(b), a distortion compensating circuit 30of the third embodiment of the invention comprises a second amplitudeinformation adjusting portion 33, a transient characteristiccompensating circuit 34 having the second amplitude informationadjusting portion 33, and a second coefficient selecting portion 35, inplace of the first amplitude information adjusting portion 13, thetransient characteristic compensating circuit 14 having the firstamplitude information adjusting portion 13, and the first coefficientselecting portion 15 in the distortion compensating circuit 10 of FIG. 1or FIG. 2.

The second amplitude information adjusting portion 33 multiplies theamplitude information r(t) by predetermined coefficient information(func2) to output amplitude information r31(t).

The second coefficient selecting portion 35 stores a table ofcoefficient information corresponding to the transmission levelinformation S1, in order to set the coefficient information (func2) ofthe second amplitude information adjusting portion 33.

The steady characteristic compensating circuit 11 stores in the memorythe AM-AM and AM-PM characteristics in the same data format as the firstembodiment of the invention, and outputs an amplitude correction signalS31 and a phase correction signal S32 while setting the output signalr31(t) from the second amplitude information adjusting portion 33, andan output signal r32(t) from the amplitude information correcting means12 as address designation signals.

The phase information correcting means 17 performs correction on thephase information θ(t) on the basis of the phase correction signal S32output from the steady characteristic compensating circuit 11, andoutputs phase information θ3(t) after correction to the orthogonalcoordinate converting means 5 or the orthogonal coordinate convertingmeans 5 b.

In the same operation as the first embodiment of the invention, theorthogonal coordinate converting means 5 of FIG. 8( a) outputs I31(t)and Q31(t) to the phase modulating means 3.

In the same operation as the first embodiment of the invention, theorthogonal coordinate converting means 5 b of FIG. 8( b) outputs I32(t)and Q32(t) to the quadrature modulating means 6.

Next, a correcting method and procedure in which the transient responsein the case where the control voltage is driven at high speed isconsidered will be described.

The second coefficient selecting portion 35 previously measures stepresponse characteristics of the power amplifier 4 during supply of acontrol voltage, and outputs the coefficient information (func2)indicated by Expression (8) to the second amplitude informationadjusting portion 33 so that r(t) and r31(t) have the relationshipindicated by Expression (7), in the case where transient responsecharacteristics are in an overshoot state as in the high outputamplitude in FIG. 4. By contrast, in the case where the responseconverges without exceeding a predetermined value during the transientresponse period as in the low output amplitude in FIG. 4, the secondcoefficient selecting portion outputs the coefficient information(func2) indicated by Expression (10) to the second amplitude informationadjusting portion 33 so that r(t) and r31(t) have the relationshipindicated by Expression (9).r(t)>r31(t)  (7)func2<1  (8)r(t)≦r31(t)  (9)func2≧1  (10)

In this way, when the address designation signal in the case where theAM-AM data stored in the steady characteristic compensating circuit 11are to be accessed is set to the amplitude information r31(t) in whichtransient response characteristics of the output signal when the controlvoltage fluctuates are considered, it is possible to obtain a desiredoutput of the power amplifier 4 even when the control voltage is drivenat high speed.

Here, the meaning of the multiplication of the coefficient information(func2) with the address designation signal will be described with usingAM-AM characteristics of the power amplifier 4.

FIG. 9 is a view showing an example of the AM-AM characteristics of thepower amplifier 4. The characteristics are varied depending on thedevice configuration and structure of the power amplifier 4.

In FIG. 9, the abscissa indicates a normalized control voltage which isnormalized with a steady control voltage at which the maximum value ofthe output amplitude is obtained, and the ordinate indicates the outputamplitude voltage of the power amplifier 4. The characteristics of thebroken line in FIG. 9 are output amplitude characteristics with respectto the steady control voltage, and the characteristics (A) and (B) shownby the solid lines in FIG. 9 are characteristics that are obtained byexecuting correction in which transient response characteristics areconsidered.

The concept of AM-AM characteristic compensation is that a controlvoltage value which is to be given as the control voltage of the poweramplifier 4 is determined in order to express the amplitude component ofa modulated signal by the output of the power amplifier 4. In the casewhere the amplitude component of a modulated signal such as shown inFIG. 26 is to be expressed, therefore, normalization is performed bymultiplying the amplitude component by a predetermined value, and thenthe reference is made coincident with the output amplitude voltage axisindicated by the ordinate of FIG. 9. The coincidence of the referencemeans that the maximum value of the amplitude signal is made coincidentwith the maximum value of the output amplitude of the power amplifier 4.Based on an amplitude values at each predetermined time interval of thesignal amplitude after the coincidence of the reference, the controlvoltage value at which the amplitude value is attained is obtained, ornamely the amplitude value is prolonged perpendicularly with theordinate of FIG. 9, and the control voltage value of the abscissa at theintersection with the characteristic curve is obtained, whereby thecontrol voltage after correction is obtained.

The characteristics (A) show the concept of correction in the case wheretransient response characteristics are in an overshoot state as in thehigh output amplitude in FIG. 4. Namely, in the case where the transientcharacteristics show overshoot characteristics, a process of reducingthe output amplitude more than the case of the steady characteristics isconducted, and hence the correction is equivalent to correctionaccording to a characteristic curve in which the inclination is largerthan the steady characteristic curve.

Next, the characteristics (B) show the concept of correction in the casewhere the response converges without exceeding a predetermined valueduring the transient response period as in the low output amplitude inFIG. 4. Namely, in the case where the response converges withoutexceeding the predetermined value during the transient response period,a process of amplifying the output amplitude more than the case of thesteady characteristics is conducted, and hence the correction isequivalent to correction according to a characteristic curve in whichthe inclination is smaller than the steady characteristic curve.

In the same manner as the first coefficient selecting portion 15,preferably, the second coefficient selecting portion 35 has aconfiguration in which a table corresponding to the input signal(|r(t)|) is prepared, and the coefficient information (func2) which isoutput in accordance with the input signal is switched over, or aconfiguration in which, in the case where the polar modulating circuitof the invention is used in a transmitting apparatus, a tablecorresponding to the transmission frequency and the environmentaltemperature is prepared, and the output coefficient information (func2)is switched over in accordance with transmission frequency informationtransmitted from the controlling portion of the transmitting apparatuswhich is not shown, temperature information from a temperature sensorwhich is not shown, or consumption current information from a circuitwhich monitors, for example, the consumption current (the collectorcurrent and the like) of the power amplifier that is equivalent to thetemperature information.

In the third embodiment of the invention, the method of, in order toavoid lowering of the transmission efficiency of a transmittingapparatus, realizing linearization of the output of the power amplifier4 with respect to a change of the control voltage without branching theoutput signal from the power amplifier 4 has been described. In the casewhere lowering of the transmission efficiency of the transmittingapparatus is allowed, or where a circuit for branching the output signalfrom the power amplifier 4 is already connected to the polar modulatingcircuit, however, the same effects can be attained also in aconfiguration where a table corresponding to the transmission levelinformation S1, the transmission frequency, and the environmentaltemperature, and the temperature sensor are not disposed, and thecoefficient information (func2) is adequately switched over while anadjacent-channel leakage power of the output spectrum of the poweramplifier 4 is directly monitored by means which is not shown, or abaseband signal after demodulation of the spectrum is monitored, or soas to minimize an error between the baseband signal and the transmissiondata.

In the above, as an effect of the transient characteristic compensatingcircuit 34, the method of realizing linearization of the output of thepower amplifier with respect to the control voltage by improving thestep response characteristics when the control voltage is applied hasbeen described.

Next, a method of simply adjusting the inclination of the AM-AMcharacteristics of the power amplifier in order to compensate thefrequency and temperature characteristics of the power amplifier, andthe like will be described.

In the cases where the frequency of the input high-frequency signal ofthe power amplifier 4 is different, and where the environmentaltemperature is changed, there is a possibility that, in addition to thetransient response characteristics, for example, the inclination itselfof the AM-AM characteristics of the power amplifier is changed.

However, the multiplying process of the second amplitude informationadjusting portion 33 constituting the transient characteristiccompensating circuit 34 is equivalent to adjustment of the inclinationof the AM-AM characteristics. Therefore, the process can be applied as amethod of adjusting the inclination of the AM-AM characteristics, andhas also effects of improving the frequency and temperaturecharacteristics.

Namely, the frequency and temperature characteristics can be improved bya configuration in which the coefficient information (func2) is preparedas a table so as to express changes of the AM-AM characteristics withrespect to the transmission frequency and the environmental temperature,and, in the case where the polar modulating circuit of the invention isused in a transmitting apparatus, the coefficient information (func2) isswitched over in accordance with transmission frequency informationtransmitted from the controlling portion of the transmitting apparatuswhich is not shown, temperature information from a temperature sensorwhich is not shown, or consumption current information from a circuitwhich monitors, for example, the consumption current (the collectorcurrent and the like) of the power amplifier that is equivalent to thetemperature information.

In the case where lowering of the transmission efficiency of thetransmitting apparatus is allowed, or where a circuit for branching theoutput signal from the power amplifier 4 is already connected to thepolar modulating circuit, the same effects can be attained also in aconfiguration where the table corresponding to the transmissionfrequency and the environmental temperature, and the temperature sensorare not disposed, and the coefficient information (func2) is adequatelyswitched over while an adjacent-channel leakage power of the outputspectrum of the power amplifier 4 is directly monitored by means whichis not shown, or a baseband signal after demodulation of the spectrum ismonitored, or so as to minimize an error between the baseband signal andthe transmission data.

Another example of the polar modulating circuit of the third embodimentof the invention may have the configuration shown in FIG. 10. FIG. 10 isa view showing the other example of the schematic configuration of thepolar modulating circuit of the third embodiment of the invention. Thepolar modulating circuit of this example is configured so that theorthogonal coordinate converting means 5 b and the phase informationcorrecting means 17 are removed away from FIG. 8( b), and the input IQsignal of the quadrature modulating means 6 is changed from I32(t),Q32(t) to an IQ signal (I(t), Q(t)) input from the baseband signalgenerating portion of the transmitting apparatus which is not shown,thereby omitting the phase correction of the phase-modulated signal.Namely, the invention shown by the third embodiment of the inventionperforms compensation only on a portion of the power amplifier 4relating to the control voltage.

In the case where the polar modulating circuit of the invention is usedin a transmitting apparatus, a DA converter which is not shown is placedbetween, in FIG. 8( a), stages of the amplitude information correctingmeans 12 and the amplitude modulating means 2, and stages of theorthogonal coordinate converting means 5 and the phase modulating means3, between, in FIG. 8( b), stages of the amplitude informationcorrecting means 12 and the amplitude modulating means 2, and stages ofthe orthogonal coordinate converting means 5 b and the quadraturemodulating means 6, and between, in FIG. 10, stages of the amplitudeinformation correcting means 12 and the amplitude modulating means 2,and in front of the quadrature modulating means 6.

As described above, according to the third embodiment of the invention,relating to distortion compensation using the AM-AM and AM-PMcharacteristics in steady characteristics to be stored in the steadycharacteristic compensating circuit 11, the address designation signalwhen the phase correction signal is to produced is multiplied by thecoefficient information (func2) expressing the transient response,whereby, in the polar modulation system, while suppressing increase ofcompensation data, amplitude/phase information relating to a modulatedsignal can be correctly expressed, or namely low-distortioncharacteristics of the power amplifier can be realized.

In the third embodiment of the invention above, the effect thatamplitude information relating to a modulated signal in datatransmission is correctly expressed has been described. It is a matterof course that starting characteristics (ramp control) of a poweramplifier which performs a burst operation can be stabilized byadjusting the coefficient information (func2) expressing the transientresponse with respect to the starting time. Therefore, a rampcontrolling circuit for a power amplifier may be configured by using thedistortion compensating circuit of the third embodiment of theinvention.

As described above, in the third embodiment of the invention, themultiplying process conducted by the second amplitude informationadjusting portion 33 is equivalent to the process of adjusting theinclination of the characteristic curve. Therefore, it is a matter ofcourse that the same effects are attained also when the multiplyingprocess conducted by the second amplitude information adjusting portion33 is previously conducted on the data stored in the steadycharacteristic compensating circuit 11.

Fourth Embodiment

A fourth embodiment of the invention describes a method which cannot besolved by related art 4, and which, in the polar modulation system,compensates a change of the phase characteristics at a signal changepoint without using a feedback system.

FIGS. 11 and 12 are views showing a schematic configuration of a polarmodulating circuit of the fourth embodiment of the invention. Theportions which are duplicated with those of the polar modulating circuitof FIG. 1 or 2 which has been described in the first embodiment of theinvention are denoted by the same reference numerals.

As shown in FIGS. 11 and 12, a distortion compensating circuit 40 of thefourth embodiment of the invention comprises a third amplitudeinformation adjusting portion 43, a phase compensating circuit 44 havingthe third amplitude information adjusting portion 43, and a thirdcoefficient selecting portion 45, in place of the first amplitudeinformation adjusting portion 13, the transient characteristiccompensating circuit 14 having the first amplitude information adjustingportion 13, and the first coefficient selecting portion 15 of thedistortion compensating circuit 10 of FIG. 1 or 2.

The third amplitude information adjusting portion 43 multiplies theoutput signal r11(t) from the amplitude information correcting means 12by predetermined coefficient information (func3) to output amplitudeinformation r4(t).

The third coefficient selecting portion 45 sets the coefficientinformation (func3) of the third amplitude information adjusting portion43.

The steady characteristic compensating circuit 11 stores in the memorythe AM-AM and AM-PM characteristics in the same data format as the firstembodiment of the invention, and outputs a phase correction signal S42with using the output signal r4(t) from the third amplitude informationadjusting portion 43 as an address designation signal. The method ofproducing the amplitude correction signal S11 is identical with thefirst embodiment of the invention, and its description is omitted.

The phase information correcting means 17 performs correction on thephase information θ(t) on the basis of the phase correction signal S42output from the steady characteristic compensating circuit 11, andoutputs phase information θ4(t) after correction to the orthogonalcoordinate converting means 5 or 5 b.

In the same operation as the first embodiment of the invention, theorthogonal coordinate converting means 5 of FIG. 11 outputs I41(t) andQ41(t) to the phase modulating means 3.

In the same operation as the first embodiment of the invention, theorthogonal coordinate converting means 5 b of FIG. 12 outputs I42(t) andQ42(t) to the quadrature modulating means 6.

In the case where the polar modulating circuit of the invention is usedin a transmitting apparatus, a DA converter which is not shown is placedbetween, in FIG. 11, stages of the amplitude information correctingmeans 12 and the amplitude modulating means 2, and stages of theorthogonal coordinate converting means 5 and the phase modulating means3, and between, in FIG. 12, stages of the amplitude informationcorrecting means 12 and the amplitude modulating means 2, and stages ofthe orthogonal coordinate converting means 5 b and the quadraturemodulating means 6.

Next, passing phase characteristics with respect to a control voltage ofan amplifier will be described.

As shown in FIG. 27 which has been described in the background art,depending on the characteristics of the power amplifier 4 and theamplitude modulating means 2, the passing phase characteristics aredifferent in the cases where the control signal is increased, and wherethe signal is decreased. In order to reduce the correction error,therefore, the phase correction must be performed in consideration ofboth the rising and falling characteristics.

In order to correct express an modulated signal, when phase correctionis executed on the basis of the rising characteristic curve (solid line)in the case where the dynamic range of r11(t) is 0.4 to 1.0 of thenormalized control voltage in FIG. 27, for example, phase correction ofabout 11° is performed between the maximum and minimum values of thecontrol voltage. By contrast, in case of phase correction on the basisof the falling characteristic curve (broken line), correction of about8° is performed in the same zone. When phase correction referring to therising characteristic curve is performed in the case where the amplitudeof the amplitude information r(t) is in the decreasing direction, acorrection error is caused.

As one simple method of reducing the correction error, it iscontemplated that the rising and falling characteristic curve areaveraged (weighted as required). In the embodiment, in considerationthat it is not easy to acquire the rising and falling characteristics, amethod of performing correction following the rising and fallingcharacteristics by using the output amplitude and phase characteristicswith respect to the control voltage in a steady state will be described.

FIG. 13 is a view showing passing phase characteristics with respect tothe control voltage in a steady state after the control voltage isinput. In FIG. 13, the abscissa indicates the normalized controlvoltage, and the ordinate indicates the passing phase rotation amount.The solid line in the figure shows passing phase characteristics withrespect to the control voltage amplitude under conditions that an inputhigh-frequency signal amplitude having a level at which the poweramplifier 4 operates in saturation is supplied. The data can be acquiredby using, for example, a network analyzer.

When the change rate of the control voltage is lowered, the risingcharacteristic curve shown in FIG. 27 is made close to thecharacteristics shown in FIG. 13. In the fourth embodiment of theinvention, therefore, description is made with referring to the risingcharacteristic curve shown by the solid line in FIG. 27 as thecharacteristic curve of the steady state shown in FIG. 13.

Hereinafter, the operation of the distortion compensating circuit 40 ofthe fourth embodiment of the invention will be described.

A case where, when the required dynamic range of r11(t) is 0.4 to 1.0 ofthe normalized control voltage in the same manner as the above example,for example, phase correction is performed by compressing (for example,a compression ratio of 20%) the dynamic range in the direction of theabscissa (control voltage) with reference to the normalized controlvoltage of 1.0 will be considered.

After compression, the dynamic range is 0.52 to 1.0. The phasecorrection of 8° is performed between the maximum and minimum values ofthe control voltage, and the characteristic curve can be made close tothe falling characteristic curve. When the coefficient information(func3) is adjusted, therefore, it is possible to, base on the risingcharacteristic curve, obtain a curve corresponding to averaging, and acurve corresponding to the falling characteristic curve.

In the fourth embodiment of the invention, the third amplitudeinformation adjusting portion 43 performs the above-mentionedcompression on the output signal r11(t) output from the amplitudeinformation correcting means 12, and outputs the amplitude informationr4(t) after compression as an address designation signal, to the steadycharacteristic compensating circuit 11. The steady characteristiccompensating circuit 11 is configured so as to output the phasecorrection signal S42 to execute phase correction on the phaseinformation θ(t) in the phase information correcting means 17.

The reference point (1.0) of normalization of the normalized controlvoltage of FIGS. 13 and 27 is a control voltage at which the maximumamplitude at a preset transmission level is output. The steadycharacteristic compensating circuit 11 performs normalization of thecontrol voltage based on the transmission level information S1.

The case where the coefficient information (func3) is constantirrespective of the instantaneous amplitude value of the amplitudeinformation r(t) has been described. When the coefficient information(func3) is adjusted based on |r(t)| output from the amplitudedetermining portion 16, it is possible to express more correctly thefalling characteristic curve from the rising characteristic curve.Preferably, the third coefficient selecting portion 45 is configured sothat the coefficient information (func3) corresponding to |r(t)| ispreviously stored, and the coefficient information (func3) is switchedover in accordance with |r(t)|. Also, a configuration in which thecoefficient information (func3) corresponding to the transmission levelinformation S1 is previously stored, and the coefficient information(func3) is switched over in accordance with the transmission levelinformation is effective.

When the coefficient information (func3) is switched over in accordancewith increase or decrease (Δr(t)) of the amplitude information r(t), itis possible to express more correctly the rising and fallingcharacteristics of the output phase with respect to the control voltage.More preferably, the embodiment is configured so that the coefficientinformation (func3) corresponding to Δr(t) is previously stored in thethird coefficient selecting portion 45, and the coefficient information(func3) is switched over in accordance with Δr(t).

Also in the cases where the frequency of the input high-frequency signalof the power amplifier 4 is different, and where the environmentaltemperature is changed, there is a possibility that the transientresponse characteristics are different. Therefore, it is furtherpreferable to have a configuration where a table corresponding to thetransmission frequency and the environmental temperature is prepared inthe third coefficient selecting portion 45, and the output coefficientinformation (func3) is switched over in accordance with transmissionfrequency information which, in the case where the polar modulatingcircuit of the invention is used in a transmitting apparatus, istransmitted from the controlling portion of the transmitting apparatuswhich is not shown, temperature information from a temperature sensorwhich is not shown, or consumption current information from a circuitwhich monitors, for example, the consumption current (the collectorcurrent and the like) of the power amplifier that is equivalent to thetemperature information.

In the fourth embodiment of the invention, the method in which, in orderto avoid lowering of the transmission efficiency of a transmittingapparatus, the output signal from the power amplifier 4 is not branchedhas been described. In the case where lowering of the transmissionefficiency of the transmitting apparatus is allowed, or where a circuitfor branching the output signal from the power amplifier 4 is alreadyconnected to the polar modulating circuit, however, the same effects canbe attained also in a configuration where a table corresponding to thetransmission frequency, and the environmental temperature, and thetemperature sensor are not disposed, and the coefficient information(func3) is adequately switched over while an adjacent-channel leakagepower of the output spectrum of the power amplifier 4 is directlymonitored by means which is not shown, or a baseband signal afterdemodulation of the spectrum is monitored, or so as to minimize an errorbetween the baseband signal and the transmission data.

As described above, in the distortion compensating circuit of the fourthembodiment of the invention, relating to distortion compensation usingthe AM-AM and AM-PM characteristics in steady characteristics to bestored in the steady characteristic compensating circuit 11, the addressdesignation signal when the phase correction signal is to produced ismultiplied by the coefficient information (func3) expressing thedifference of the AM-PM characteristics with respect to rising/fallingcontrol signals, whereby, in the polar modulation system, whilesuppressing increase of compensation data, phase information can becorrectly expressed, or namely low-distortion characteristics of thepower amplifier can be realized even when a phase change occurs at asignal change point of the modulated signal.

With respect to the delaying means and feedback system which areproblems in related art 4, in the fourth embodiment of the invention,the former is unnecessary, and the latter is not essential. Incompensation of the AM-PM characteristics at a signal change point,therefore, the circuit scale can be reduced as compared with related art4.

When the distortion compensation of the fourth embodiment of theinvention which uses the coefficient information (func3) expressing thedifference of the AM-PM characteristics with respect to rising/fallingcontrol signals is applied to FIGS. 1 and 2 of the first embodiment ofthe invention, FIGS. 6 and 7 of the second embodiment of the invention,and FIGS. 8( a) and 8(b) of the third embodiment of the invention,further low-distortion characteristics of the power amplifier can berealized.

In the fourth embodiment of the invention, the case where a networkanalyzer is used is described as the method of acquiring data which areorigins of the stored data to the steady characteristic compensatingcircuit 11. However, it is a matter of course that characteristics ofthe power amplifier 4 may be acquired by other measuring means.

In the fourth embodiment of the invention, the method of adjusting theAM-PM characteristics has been described. The adjustment of the AM-PMcharacteristics has the same function as that of adjustingsynchronization between the amplitude signal and the phase signal. Whenthe coefficient information (func3) is switched over, therefore, theembodiment can be applied also to the adjustment of synchronizationbetween the amplitude signal and the phase signal. In the description ofthe method of adjusting the AM-PM characteristics, the example in whichthe required dynamic range for the control voltage is compressed hasbeen used. It is a matter of course that not only a case of compressionbut also a case of expansion may exist in the adjustment ofsynchronization.

Fifth Embodiment

A fifth embodiment of the invention describes a method which cannot besolved by related art 4, which, in the polar modulation system,compensates a change of the phase characteristics at a signal changepoint without using a feedback system, and which is different from thefourth embodiment of the invention.

FIGS. 14 and 15 are views showing a schematic configuration of a polarmodulating circuit of the fifth embodiment of the invention. Theportions which are duplicated with those of FIGS. 8( a) and 8(b) whichhave been described in the third embodiment of the invention are denotedby the same reference numerals.

As shown in FIGS. 14 and 15, a distortion compensating circuit 50 of thefifth embodiment of the invention comprises a steady characteristiccompensating circuit 11 b, a fourth amplitude information adjustingportion 53, a transient characteristic/phase compensating circuit 54having the fourth amplitude information adjusting portion 53, and afourth coefficient selecting portion 55, in place of the steadycharacteristic compensating circuit 11, the second amplitude informationadjusting portion 33, the transient characteristic compensating circuit34 having the second amplitude information adjusting portion 33, and thesecond coefficient selecting portion 35 in the distortion compensatingcircuit 30 of FIGS. 8( a) and 8(b).

The fourth amplitude information adjusting portion 53 multiplies theamplitude information r(t) by two predetermined independent coefficientinformation (func2) and coefficient information (func4) to outputamplitude information r31(t) and amplitude information r51(t).

The fourth coefficient selecting portion 55 sets the two independentcoefficient information (func2) and coefficient information (func4) ofthe fourth amplitude information adjusting portion 53.

In the same manner as the steady characteristic compensating circuit 11of the first embodiment of the invention, the steady characteristiccompensating circuit 11 b stores, as the AM-AM characteristics, data inthe absolute value format of the control voltage with respect to theoutput signal amplitude, or the predetermined value (data in the formatof a difference value) which, after the input control signal amplitudeis multiplied or divided by the above-mentioned predetermined value, isnormalized with the input control signal so as to attain the absolutevalue, from output signal amplitude characteristics and passing phasecharacteristics of a fundamental wave component with respect to thecontrol voltage (steady state) of the power amplifier 4, in the casewhere an unmodulated one-carrier which can be acquired by using anetwork analyzer and the like, and which has a constant level (constantvalue) is input as a high-frequency input signal to the power amplifier4.

From the output signal amplitude characteristics and passing phasecharacteristics with respect to the control voltage, the AM-PMcharacteristics are stored in the format different from the format ofthe passing phase characteristic data with respect to the controlvoltage in the steady characteristic compensating circuit 11 of thefirst embodiment of the invention, or namely in the format of thepassing phase characteristic data with respect to the output signalamplitude. This is equal to the case where the abscissa of FIG. 13 isreplaced with the output signal amplitude.

The relationships of input and output signals in the steadycharacteristic compensating circuit 11 b output an amplitude correctionsignal S31 and a phase correction signal S52 while, as addressdesignation signals, using the amplitude information r31(t) and r51(t)output from the fourth amplitude information adjusting portion 53. Thesteady characteristic compensating circuit 11 b performs a process ofnormalizing the AM-AM and AM-PM characteristics based on thetransmission level information S1.

Specifically, based on the maximum transmission power in which themaximum value—the average value (peak factor) of amplitude informationcorresponding to the modulation system is considered, normalization ofan output signal amplitude in stored AM-AM data and AM-PM data isexecuted on a desired output level (average power), whereby correctionis performed for each desired output level. As a result of thenormalization, access to AM-AM data and AM-PM data with using theamplitude information r31(t) and r51(t) as an address designation signalis enabled.

The phase information correcting means 17 performs correction on thephase information θ(t) on the basis of the phase correction signal S52output from the steady characteristic compensating circuit 11 b, andoutputs phase information θ5(t) after correction to the orthogonalcoordinate converting means 5 or 5 b.

In the same operation as the first embodiment of the invention, theorthogonal coordinate converting means 5 of FIG. 14 outputs I51(t) andQ51(t) to the phase modulating means 3.

In the same operation as the first embodiment of the invention, theorthogonal coordinate converting means 5 b of FIG. 15 outputs I52(t) andQ52(t) to the quadrature modulating means 6.

A DA converter which is not shown is placed between, in FIG. 14, stagesof the amplitude information correcting means 12 and the amplitudemodulating means 2, and stages of the orthogonal coordinate convertingmeans 5 and the phase modulating means 3, and between, in FIG. 15,stages of the amplitude information correcting means 12 and theamplitude modulating means 2, and stages of the orthogonal coordinateconverting means 5 b and the quadrature modulating means 6.

As described above, in the fifth embodiment of the invention, ascompared with the third embodiment of the invention, the manner ofgiving the address designation signal when the phase correction signalis to produced, and the data format of the AM-AM characteristics to bestored into the steady characteristic compensating circuit due to thischange are different. Here, only the portions different from those ofthe third embodiment of the invention will be described, and thedescription of the common portions is omitted.

The fifth embodiment of the invention describes a method which isdifferent from the fourth embodiment of the invention, and in which thephase correction is performed in consideration of both the rising andfalling characteristics in correspondence that, as described in thefourth embodiment of the invention, passing phase characteristics aredifferent in the cases where the control signal is increased, and wherethe signal is decreased, because of the characteristics of the poweramplifier 4 and the amplitude modulating means 2.

In the fifth embodiment of the invention, the configuration in which theamplitude signal r(t) corresponding to the output signal amplitude isobtained, and the r(t) is multiplied by the predetermined constant(func4) to compress the dynamic range of the amplitude signal exerts thesame effects as the fourth embodiment of the invention in which thedynamic range of the address designation signal is compressed.

With respect to the delaying means and feedback system which areproblems in related art 4, in the fifth embodiment of the invention, theformer is unnecessary, and the latter is not essential. In compensationof the AM-PM characteristics at a signal change point, therefore, thecircuit scale can be reduced as compared with related art 4.

Next, the compression method in the fifth embodiment of the inventionwill be specifically described.

In the fourth embodiment of the invention, with reference to the maximumvalue of the required dynamic range for the normalized control voltage,compression is performed in the direction of the maximum value. In thefifth embodiment of the invention, the normalized control voltage isreplaced with the amplitude signal r(t) corresponding to the outputsignal amplitude. Namely, the amplitude signal r(t) is multiplied by thecoefficient information (func4) indicated by Expression (11) so that,with reference to the maximum value of the required dynamic range forthe amplitude signal r(t), compression is performed in the direction ofthe maximum value.func4<1  (11)

As described above, according to the fifth embodiment of the invention,relating to distortion compensation using the AM-AM and AM-PMcharacteristics in steady characteristics to be stored in the steadycharacteristic compensating circuit 11 b, the amplitude correctionsignal and the address designation signal when the phase correctionsignal is produced are multiplied with the coefficient information(func2) and coefficient information (func4) expressing the transientresponse and signal change point characteristics, whereby, in the polarmodulation system, while suppressing increase of compensation data,amplitude/phase information relating to a modulated signal can becorrectly expressed, or namely low-distortion characteristics of thepower amplifier can be realized.

In the fifth embodiment of the invention, the effect that amplitudeinformation relating to a modulated signal in data transmission iscorrectly expressed has been described. It is a matter of course thatstarting characteristics (ramp control) of a power amplifier whichperforms a burst operation can be stabilized by adjusting thecoefficient information (func2) expressing the transient response withrespect to the starting time. Therefore, a ramp controlling circuit fora power amplifier may be configured by using the distortion compensatingcircuit of the fifth embodiment of the invention.

In the fifth embodiment of the invention, it is a matter of course thatthe same effects are attained also when the multiplying processconducted by the fourth amplitude information adjusting portion 53 ispreviously conducted on the data stored in the steady characteristiccompensating circuit 11 b.

In the fifth embodiment of the invention, the method of adjusting theAM-PM characteristics has been described. The adjustment of the AM-PMcharacteristics has the same function as that of adjustingsynchronization between the amplitude signal and the phase signal. Whenthe coefficient information (func4) is switched over, therefore, theembodiment can be applied also to the adjustment of synchronizationbetween the amplitude signal and the phase signal. In the description ofthe method of adjusting the AM-PM characteristics, the example in whichthe required dynamic range for the control voltage is compressed hasbeen used. It is a matter of course that not only a case of compressionbut also a case of expansion may exist in the adjustment ofsynchronization.

Sixth Embodiment

A sixth embodiment of the invention shows that a combination of thepolar modulating circuit of the first embodiment of the invention andthe polar modulating circuit of the fifth embodiment of the inventioncan be configured.

FIGS. 16 and 17 are views showing a schematic configuration of a polarmodulating circuit of the sixth embodiment of the invention. Theportions which are duplicated with those of FIGS. 1, 2, 14, and 15 whichhave been described in the first and fifth embodiments of the inventionare denoted by the same reference numerals.

As shown in FIGS. 16 and 17, a distortion compensating circuit 60 of thesixth embodiment of the invention further comprises the first amplitudeinformation adjusting portion 13, the transient characteristiccompensating circuit 14 having the first amplitude information adjustingportion 13, and the first coefficient selecting portion 15 which areshown in FIGS. 1 and 2, in addition to the circuit configuration of FIG.15.

The first amplitude information adjusting portion 13 multiplies theoutput signal r32(t) from the amplitude information correcting means 12by predetermined coefficient information (funclb) to output amplitudeinformation r61(t) to the amplitude modulating means 2. The setting ofthe coefficient information (func1 b) is in the same concept as thecoefficient information (func1) in the first embodiment of theinvention, and its description is omitted.

In the distortion compensating circuit 60, a transient responsecorrection parameter of the AM-AM characteristics of the power amplifier4 is dispersed into the first amplitude information adjusting portionand the fourth amplitude information adjusting portion, whereby thecorrection error can be reduced more than the first and fifthembodiments of the invention.

Another example of the polar modulating circuit of the sixth embodimentof the invention may have the configuration shown in FIG. 18. FIG. 18 isa view showing the other example of the schematic configuration of thepolar modulating circuit of the sixth embodiment of the invention. Thepolar modulating circuit of the example is configured so that theorthogonal coordinate converting means 5 b and the phase informationcorrecting means 17 are removed away from FIG. 17, and the input IQsignal of the quadrature modulating means 6 is changed from I52(t),Q52(t) to an IQ signal (I(t), Q(t)) input from the baseband signalgenerating portion of the transmitting apparatus which is not shown,thereby omitting the phase correction of the phase-modulated signal.

In the case where the polar modulating circuit of the invention is usedin a transmitting apparatus, a DA converter which is not shown is placedbetween, in FIG. 16, stages of the first amplitude information adjustingportion 13 and the amplitude modulating means 2, and stages of theorthogonal coordinate converting means 5 and the phase modulating means3, between, in FIG. 17, stages of the first amplitude informationadjusting portion 13 and the amplitude modulating means 2, and stages ofthe orthogonal coordinate converting means 5 b and the quadraturemodulating means 6, and between, in FIG. 18, stages of the firstamplitude information adjusting portion 13 and the amplitude modulatingmeans 2, and in front of the quadrature modulating means 6.

Seventh Embodiment

A seventh embodiment of the invention describes a method which relatesto a method of setting the output power level of the power amplifier 4,and which is different from the first to sixth embodiments of theinvention.

FIGS. 19 and 20 are views showing a schematic configuration of a polarmodulating circuit of the seventh embodiment of the invention. Theportions which are duplicated with those of FIGS. 16 and 17 which havebeen described in the sixth embodiment of the invention are denoted bythe same reference numerals.

As shown in FIGS. 19 and 20, a distortion compensating circuit 70 of theseventh embodiment of the invention comprises a steady characteristiccompensating circuit 11 c in place of the steady characteristiccompensating circuit 11 b of FIGS. 16 and 17, and further comprises amultiplying circuit 71.

The multiplying circuit 71 obtains a level control coefficient (S1/S0)which is obtained by dividing the transmission level information S1 by areference value S0 of the transmission level information S1. The levelcontrol coefficient is multiplied to the output amplitude informationr(t) of the polar coordinate converting means 1 to output amplitudeinformation r71(t) on which the transmission level information issuperimposed.

The fourth amplitude information adjusting portion 53 multiplies theamplitude information r71(t) by two predetermined independentcoefficient information (func5) and coefficient information (func6) tooutput amplitude information r72(t) and amplitude information r73(t).The settings of the coefficient information (func5) and the coefficientinformation (func6) are identical respectively with the setting methodsof the coefficient information (func2) and the coefficient information(func4), and their description is omitted.

The steady characteristic compensating circuit 11 c sets as a referenceof the address designation signal for stored data, the AM-AM and AM-PMcharacteristics corresponding to the maximum transmission power S0 b(when S0 is in dB unit, S0 b=S0+3.2 [dB]) in which, for example, a peakfactor (for example, 3.2 [dB] in 8-PSK modulation) for each modulationsystem is considered with respect to the reference value S0 of thetransmission level information. As data in the same data format as thesteady characteristic compensating circuit 11 b of the fifth embodimentof the invention, i.e., data in the absolute value format of the controlvoltage with respect to the output signal amplitude, as the AM-AMcharacteristics, or a predetermined value (data in the format of adifference value) which, after the input control signal amplitude ismultiplied or divided by the above-mentioned predetermined value, isnormalized with the input control signal so as to attain the absolutevalue are stored in a memory. Furthermore, as the AM-PM characteristics,data in the format of the passing phase characteristic data with respectto the output signal amplitude are stored in the memory. Therelationships of input and output signals in the steady characteristiccompensating circuit 11 c output an amplitude correction signal S71 anda phase correction signal S72 while, as address designation signals,using r72(t) and r73(t) output from the fourth amplitude informationadjusting portion 53.

The amplitude information correcting means 12 performs correction on theamplitude information r71(t) output from the multiplying circuit 71, onthe basis of the amplitude correction signal S71 output from the steadycharacteristic compensating circuit 11 c, and outputs amplitudeinformation r74(t).

The first amplitude information adjusting portion 13 multiplies theamplitude information r74(t) output from the amplitude informationcorrecting means 12 by predetermined coefficient information (func1 c)to output amplitude information r75(t). The setting of the coefficientinformation (func1 c) is in the same concept as the coefficientinformation (func1) in the first embodiment of the invention, and itsdescription is omitted.

The amplitude determining portion 16 has functions of calculating aninstantaneous amplitude value (|r71(t)|) of the amplitude informationr71(t) sampled at constant intervals, and setting a predeterminedthreshold based on the plural instantaneous amplitude values anddetermining increase or decrease (Δr71(t)) of the amplitude informationr71(t) from a previous sampling timing.

The phase information correcting means 17 performs correction on thephase information θ(t) on the basis of the phase correction signal S72output from the steady characteristic compensating circuit 11, andoutputs phase information θ5(t) after correction to the orthogonalcoordinate converting means 5 or 5 b.

In the same operation as the first embodiment of the invention, theorthogonal coordinate converting means 5 of FIG. 19 outputs I71(t) andQ71(t) to the phase modulating means 3.

In the same operation as the first embodiment of the invention, theorthogonal coordinate converting means 5 b of FIG. 20 outputs I72(t) andQ72(t) to the quadrature modulating means 6.

As described above, the seventh embodiment of the invention describesthe method of setting the output level of the power amplifier 4, andparticularly the method which is different from the method of settingthe output level in the first to sixth embodiments of the invention.Specifically, in the first to fourth embodiments of the invention andthe fifth and sixth embodiments of the invention, the steadycharacteristic compensating circuit 11 or 11 b obtains the maximumtransmission power in which the maximum value—the average value (peakfactor) of amplitude information for each modulation system isconsidered, from the desired output level (average power) correspondingto the transmission level information S1, and normalization of thestored data with reference to the maximum transmission power isexecuted, whereby correction is performed for each desired output level.By contrast, the seventh embodiment of the invention is different inthat data themselves which are to be stored in the steady characteristiccompensating circuit 11 c are configured in consideration of the powercontrol, and distortion compensation at a desired output level isperformed by using amplitude information (r72(t), r73(t)) on which thetransmission level information using the level control coefficient issuperimposed, as the address designation signal.

Another example of the polar modulating circuit of the seventhembodiment of the invention may have the configuration shown in FIG. 21.FIG. 21 is a view showing the other example of the schematicconfiguration of the polar modulating circuit of the seventh embodimentof the invention. The polar modulating circuit of the example isconfigured so that the orthogonal coordinate converting means 5 b andthe phase information correcting means 17 are removed away from FIG. 20,and the input IQ signal of the quadrature modulating means 6 is changedfrom I72(t), Q72(t) to an IQ signal (I(t), Q(t)) input from the basebandsignal generating portion of the transmitting apparatus which is notshown, thereby omitting the phase correction of the phase-modulatedsignal.

In the case where the polar modulating circuit of the invention is usedin a transmitting apparatus, a DA converter which is not shown is placedbetween, in FIG. 19, stages of the first amplitude information adjustingportion 13 and the amplitude modulating means 2, and stages of theorthogonal coordinate converting means 5 and the phase modulating means3, between, in FIG. 20, stages of the first amplitude informationadjusting portion 13 and the amplitude modulating means 2, and stages ofthe orthogonal coordinate converting means 5 b and the quadraturemodulating means 6, and between, in FIG. 21, stages of the firstamplitude information adjusting portion 13 and the amplitude modulatingmeans 2, and in front of the quadrature modulating means 6.

Eighth Embodiment

An eighth embodiment of the invention describes a method of improvingthe control accuracy which is shown in related art 5, or which is aproblem in the output linearizing technique during a low-output power ina power amplifier.

FIGS. 22 and 23 are views showing a schematic configuration of a polarmodulating circuit of the eighth embodiment of the invention. Theportions which are duplicated with those of FIGS. 19 and 20 which havebeen described in the seventh embodiment of the invention are denoted bythe same reference numerals.

As shown in FIGS. 22 and 23, a distortion compensating circuit 80 of theeighth embodiment of the invention comprises a steady characteristiccompensating circuit 11 d in place of the steady characteristiccompensating circuit 11 c of FIG. 20, and further comprises an amplitudeadjusting portion 81 and a fifth coefficient selecting portion 82.

The eighth embodiment of the invention describes a method of simplyreducing the input signal amplitude in accordance with reduction of theoutput signal amplitude of the power amplifier 4.

The amplitude adjusting portion 81 multiplies the amplitude of theoutput IQ signal from the orthogonal coordinate converting means 5 or 5b by predetermined coefficient information (func10), and outputs the IQsignal in which the amplitude is adjusted.

The fifth coefficient selecting portion 82 sets the coefficientinformation (func10) of the amplitude adjusting portion 81, andtransmits the coefficient information to the steady characteristiccompensating circuit 11 d.

The quadrature modulating means 6 performs quadrature modulation basedon the IQ signal output from the amplitude adjusting portion 81.

Transmission level information S1 is transmission level information ofthe power amplifier 4 which, in the case where the polar modulatingcircuit of the invention is used in a transmitting apparatus, istransmitted from a controlling portion of the transmitting apparatuswhich is not shown. The information is input into the multiplyingcircuit 71 and the first, fourth, and fifth coefficient selectingportions 15, 55, 82.

The steady characteristic compensating circuit 11 d stores in a memorycompensation data which are produced based on the AM-AM and AM-PMcharacteristics that are acquired in plural input high-frequency signalamplitudes, in the same data format as the steady characteristiccompensating circuit 11 b of the fifth embodiment of the invention,i.e., as the AM-AM characteristics, data in the absolute value format ofthe control voltage with respect to the output signal amplitude, or apredetermined value (data in the format of a difference value) which,after the input control signal amplitude is multiplied or divided by theabove-mentioned predetermined value, is normalized with the inputcontrol signal so as to attain the absolute value, and stores in thememory passing phase characteristic data with respect to the outputsignal amplitude as the AM-PM characteristics.

Based on the coefficient information (func10) from the fifth coefficientselecting portion 82, the amplitude of the input high-frequency signalto the power amplifier 4 during transmission operation is determined,data which are acquired at an adequate amplitude value are selected fromthe AM-AM and AM-PM characteristics which are acquired at plural inputhigh-frequency signal amplitudes, and compensation is performed. Therelationships of input and output signals in the steady characteristiccompensating circuit 11 d output an amplitude correction signal S81 anda phase correction signal S82 while, as address designation signals,using r81(t) and r82(t) output from the fourth amplitude informationadjusting portion 53.

When the amplitude of the input IQ signal of the quadrature modulatingmeans 6 is controlled, it is possible to control the output power of thequadrature modulating means 6, i.e., the input power of the poweramplifier 4. When the output power of the power amplifier 4 is to belowered, therefore, the fifth coefficient selecting portion 82 transmitscoefficient information (func10(1)) which is smaller than coefficientinformation (func10(h)) during high output, to the amplitude adjustingportion 81 on the basis of the transmission level information S1 whichis a parameter for controlling the power. In the amplitude adjustingportion 81, the output signal from the orthogonal coordinate convertingmeans 5 or 5 b is multiplied by the coefficient information, and theresulting signal is transmitted to the quadrature modulating means 6.

Simultaneously with switching of the coefficient information (func10),the steady characteristic compensating circuit 11 d selects one datagroup from data groups which have the same amplitude of the inputhigh-frequency signal of the power amplifier 4 during data acquisition.

Another example of the polar modulating circuit of the eighth embodimentof the invention may have the configuration shown in FIG. 24. FIG. 24 isa view showing the other example of the schematic configuration of thepolar modulating circuit of the eighth of the invention. The polarmodulating circuit of the example is configured so that the orthogonalcoordinate converting means 5 b and the phase information correctingmeans 17 are removed away from FIG. 23, and the input IQ signal of thequadrature modulating means 6 is changed from I84(t), Q84(t) to I85(t),Q85(t) in which an IQ signal (I(t), Q(t)) input from the baseband signalgenerating portion of the transmitting apparatus which is not shown ismultiplied by the coefficient information (func10) in the amplitudeadjusting portion 81, thereby omitting the phase correction of thephase-modulated signal.

In the case where the polar modulating circuit of the invention is usedin a transmitting apparatus, a DA converter which is not shown is placedbetween, in FIG. 22, stages of the first amplitude information adjustingportion 13 and the amplitude modulating means 2, and stages of theamplitude adjusting portion 81 and the quadrature modulating means 6,between, in FIG. 23, stages of the first amplitude information adjustingportion 13 and the amplitude modulating means 2, and stages of theamplitude adjusting portion 81 and the quadrature modulating means 6,and between, in FIG. 24, stages of the first amplitude informationadjusting portion 13 and the amplitude modulating means 2, and stages ofthe amplitude adjusting portion 81 and the quadrature modulating means6.

As described above, in the eighth embodiment of the invention, theconfiguration in which the signal amplitude of the baseband ismultiplied by the predetermined coefficient information (func10), andthe coefficient information is switched over can reduce the amplitude ofthe input signal to the power amplifier 4 in accordance with reductionof the output signal amplitude of the power amplifier 4. Simultaneouslywith the switching, compensation data to be referred are switched over.According to the configuration, the timing of switching over a parameterduring the power control can be set to a synchronizing timing, and thecontrol can be simplified. Furthermore, the calculating process isconducted in a digital signal processing portion, and the embodimentdoes not have amplitude controlling means by a high-frequency bandcircuit which is the problem of related art 5. Therefore, a highlyaccurate control is enabled.

In the eighth embodiment of the invention, the method in which, in orderto avoid lowering of the transmission efficiency of a transmittingapparatus, the output signal from the power amplifier 4 is not branchedhas been described. In the case where lowering of the transmissionefficiency of the transmitting apparatus is allowed, or where a circuitfor branching the output signal from the power amplifier 4 is alreadyconnected to the polar modulating circuit, and in the case where anerror is caused in the amplitude of the input high-frequency signal ofthe power amplifier 4 during acquisition of the compensation data of thepower amplifier 4 stored in the steady characteristic compensatingcircuit 11 d, and during transmission operation, the coefficientinformation (func10) is finely adjusted while an adjacent-channelleakage power of the output spectrum of the power amplifier 4 isdirectly monitored by means which is not shown, or a baseband signalafter demodulation of the spectrum is monitored, or so as to minimize anerror between the baseband signal and the transmission data, whereby thecompensation accuracy can be improved.

Ninth Embodiment

The ninth embodiment of the invention describes a method of reducingnoises output from a transmitting apparatus.

FIG. 25 is a view showing a schematic configuration of a polarmodulating circuit of the ninth embodiment of the invention. As shown inFIG. 25, in the polar modulating circuit of the ninth embodiment of theinvention, the first amplitude information adjusting portion 13, thetransient characteristic compensating circuit 14 having the firstamplitude information adjusting portion 13, and the first coefficientselecting portion 15 are removed away from FIG. 22 of the eighthembodiment of the invention, and the circuit has a fifth amplitudeinformation adjusting portion 53 b and a sixth coefficient selectingportion 55 b in place of the fourth amplitude information adjustingportion 53 and the fourth coefficient selecting portion 55 of FIG. 22,and a distortion compensating circuit 90 which further comprises alow-pass filter 91 and a band selecting portion 92. The description ofthe portions which are duplicated with those of the contents describedin the eighth embodiment of the invention is omitted.

The fifth amplitude information adjusting portion 53 b multiplies theamplitude information r71(t) by two predetermined independentcoefficient information (func5) and coefficient information (func6 b) tooutput amplitude information r81(t) and amplitude information r91(t).The method of setting the coefficient information (func5) has beendescribed in the seventh embodiment of the invention, and itsdescription is omitted. The method of setting the coefficientinformation (func6 b) will be described later.

The sixth coefficient selecting portion 55 b sets the two independentcoefficient information (func5) and coefficient information (func6 b) ofthe fifth amplitude information adjusting portion 53 b.

The relationships of input and output signals in the steadycharacteristic compensating circuit 11 d output an amplitude correctionsignal S81 and a phase correction signal S82 b while, as addressdesignation signals, using r81(t) and r91(t) output from the fifthamplitude information adjusting portion 53 b.

The phase information correcting means 17 performs correction on thephase information θ(t) on the basis of the phase correction signal S82 boutput from the steady characteristic compensating circuit 11 b, andoutputs phase information θ7 b(t) after correction to the orthogonalcoordinate converting means 5.

In the same operation as the first embodiment of the invention, theorthogonal coordinate converting means 5 outputs I81 b(t) and Q81 b(t)to the amplitude adjusting portion 81.

In the same operation as the eighth embodiment of the invention, theamplitude adjusting portion 81 produces an IQ signal (I82 b(t), Q82b(t)), and outputs the signal to the low-pass filter 91.

The low-pass filter 91 is a low-pass filter having a variable cutofffrequency (hereinafter, abbreviated to fc), changes the fc in accordancewith a control signal from the band selecting portion 92, and outputs anIQ signal in which a frequency component of the attenuation band isremoved from the IQ signal (I82 b(t), Q82 b(t)), to the quadraturemodulating means 6.

On the basis of the transmission level information S1, the bandselecting portion 92 transmits the control signal for changing the fc ofthe low-pass filter 91, to the low-pass filter 91.

In the case where the polar modulating circuit of the invention is usedin a transmitting apparatus, a DA converter which is not shown is placedbetween, in FIG. 25, stages of the amplitude information correctingmeans 12 and the amplitude modulating means 2, and stages of thelow-pass filter 91 and the quadrature modulating means 6.

Next, the operation of the thus configured distortion compensatingcircuit 90 will be described.

Prior to the description of the operation, problems which may possiblyoccur in the case where the amplitude of the input IQ signal of thequadrature modulating means 6 is reduced will be described.

For example, for uplink transmission of a mobile station in the GSMsystem, there is an absolute value regulation relating to the radiationpower level of an unwanted signal to the downlink reception band of amobile station. This regulation is an item to which attention is usuallypaid as a reception-band noise regulation in design of a transmittingportion of a mobile station.

In a transmitting apparatus in which the quadrature modulation system isemployed, as shown in JP-A-2003-152563, a low-pass filter is placed in afront stage of the quadrature modulating means 6, and high-frequencynoises are removed away from noises which are superimposed on thequadrature IQ signal till the DA converter, whereby reception-bandnoises can be reduced. In a transmitting apparatus in which the polarmodulation system is employed, by contrast, because a quadrature IQsignal is separated into an amplitude signal and a phase signal, therequired band width is four times or more as compared with a usualbaseband IQ signal, and the fc of the low-pass filter 91 which is setfor reducing reception-band noises is higher than that of a transmittingapparatus in which the quadrature modulation system is employed.

In the quadrature modulating means 6, the amplitude of an input basebandIQ signal must be optimized so as to satisfy the reception-band noiseregulation, the adjacent-channel leakage power regulation, and themodulation accuracy. Specifically, because a cause for adding noises tonoises which are removed away by a digital filter can be reduced, andinfluence of quantization noises in the DA converter can be reduced, thelarger amplitude of the input baseband IQ signal input to the quadraturemodulating means 6 is better. By contrast, in order to improve theadjacent-channel leakage power and the modulation accuracy, the loweramplitude of the baseband IQ signal is more preferable. Therefore, theamplitude of the baseband IQ signal is set to a value which is themaximum level in a range which can satisfy the adjacent-channel leakagepower regulation.

In the case where optimization is executed for transmission at themaximum power, when the amplitude if the baseband IQ signal of thequadrature modulating means 6 is reduced during transmission at a lowoutput power, the apparatus is used at an operating point which isdeviated from the optimum point. Because the cause for adding noises tonoises which are removed away by a digital filter is increased, andquantization noises in the DA converter are increased, there is apossibility that the level of reception-band noises is increase althoughthe output level of a desired signal is reduced. In a transmittingportion of a mobile station in which the margin for the reception-bandnoise regulation is small, if an uplink transmission power control isexecuted, the reception-band noise regulation cannot be satisfied.

Therefore, the distortion compensating circuit 90 of the ninthembodiment of the invention has a configuration in which, duringtransmission at an output power that is lower than that of transmissionat the maximum output power, the fc of the low-pass filter 91 islowered, and the demerit in the case where the amplitude of the basebandIQ signal is reduced during a low output power is eliminated.Specifically, the band selecting portion 92 compares S1(max) during themaximum transmission level with the transmission level information S1.If the difference between S1(max) and S1 is smaller than a predeterminedthreshold, the band selecting portion transmits a control signal offc(1) to the low-pass filter 91 to set the fc of the low-pass filter tofc(1). By contrast, if the difference between S1(max) and S1 is equal toor larger than the predetermined threshold, the band selecting portiontransmits a control signal of fc(2) which is smaller than fc(1) to thelow-pass filter 91 to set the fc of the low-pass filter to fc(2).

When the fc of the filter placed in a phase signal passage is changed,the synchronization between the amplitude signal and the phase signal islost, and both the modulation accuracy and the adjacent-channel leakagepower are impaired. Therefore, the ninth embodiment of the inventionfurther has a configuration where the method of adjusting the AM-PMcharacteristics which has been described in the fifth embodiment of theinvention is used as a synchronization adjusting method.

Next, the synchronization adjusting method will be specificallydescribed together with the method of setting the coefficientinformation (func6 b).

The same threshold as that by which the band selecting portion 92switches over the fc of the low-pass filter 91 is set. The sixthcoefficient selecting portion 55 b compares S1(max) during the maximumtransmission level with the transmission level information S1. If thedifference between S1(max) and S1 is smaller than the predeterminedthreshold, coefficient information (func6 b(1)) is transmitted to thefifth amplitude information adjusting portion 53 b.

By contrast, if the difference between S1(max) and S1 is equal to orlarger than the predetermined threshold, coefficient information (func6b(2)) which is different from the coefficient information (func6 b(1))is transmitted to the fifth amplitude information adjusting portion 53b.

As described above, when the coefficient information which is to bemultiplied with the address designation signal for the AM-PMcharacteristics is switched over in the fifth amplitude informationadjusting portion 53 b, it is possible to adjust phase information. As aresult, the synchronization between the amplitude signal and the phasesignal is adjusted.

In the ninth embodiment of the invention, the amplitude adjustingportion 81 is a digital multiplying circuit, and the low-pass filter 91is a digital filter. However, it is a matter of course that, even whenthe amplitude adjusting portion 81 is configured so as to, for example,adjust an output DC value of a DA converter or to be a reliableattenuator realized by an analog circuit, or when the low-pass filter 91is an analog filter, the same effects are attained.

Finally, it is a matter of course that, when the nine embodiments of theinvention are mutually combined, more accurate compensation is enabled.

When the polar modulating circuit described in the embodiments is formedon, for example, a silicon semiconductor substrate, the circuit can beconfigured as an integrated circuit.

When the IQ signal of the baseband signal generating portion whichproduces an arbitrary IQ signal is input to the polar coordinateconverting means 1, and the output of the power amplifier 4 is connectedto the antenna, the polar modulating circuit described in theembodiments can be configured as a transmitting apparatus.

While the invention has been described in detail and referring to thespecific embodiments, it is obvious to those skilled in the art thatvarious changes and modifications may be applied without departing thespirit and scope of the invention.

The application is based on Japanese Patent Application (No.2004-191342) filed Jun. 29, 2004, Japanese Patent Application (No.2004-361591) filed Dec. 14, 2004, and Japanese Patent Application (No.2005-132398) filed Apr. 28, 2005, and their disclosure is incorporatedherein by reference.

INDUSTRIAL APPLICABILITY

The distortion compensating circuit of the invention has an effect that,in the polar modulation system, while suppressing increase ofcompensation data and increase of the circuit scale, a modulated signalcan be correctly expressed, or low-distortion characteristics of a poweramplifier can be realized, and is useful in a ramp controlling circuit,a polar modulating circuit, a transmitting apparatus, etc.

1. A polar modulating circuit comprising: a polar coordinate convertingportion which produces an amplitude signal and a phase signal from abaseband quadrature signal that is produced from transmission data; adistortion compensation processing portion which includes a memoryportion for storing predistortion distortion compensating process datafor a predetermined phase correcting process and outputting an phasecorrection signal for correcting the phase signal, and a phasecompensating circuit for phase compensation; an amplitude modulatingportion which produces an amplitude-modulated signal based on theamplitude signal; a phase modulating portion which produces aphase-modulated signal in a radio-frequency band based on a phase signalcorrected by using the phase correction signal output from the memoryportion; and an amplifying portion into which the phase-modulated signalis input as an input high-frequency signal and the amplitude-modulatedsignal is input as a control signal, thereby producing transmission datain the radio-frequency band, wherein the phase compensating circuitperforms the phase compensation by adjusting amplitude of an addressdesignation signal when the phase correction signal is output from thememory or adjusting an amplitude of the phase-modulated signal input tothe amplifying portion as the input high-frequency signal.
 2. The polarmodulating circuit according to claim 1, wherein the distortioncompensation processing portion includes: a calculating circuit whichmultiplies or adds a predetermined coefficient to the amplitude signal;and a coefficient selecting portion which sets the coefficient to becalculation-processed in the calculating circuit.
 3. The polarmodulating circuit according to claim 2, wherein the coefficientselecting portion switches over the coefficient in accordance with atransmission output power.
 4. The polar modulating circuit according toclaim 2, wherein the coefficient selecting portion switches over thecoefficient in accordance with a frequency of an input signal of theamplifying portion.
 5. The polar modulating circuit according to claim2, further comprising an environmental temperature detecting portion,wherein the coefficient selecting portion switches over the coefficientin accordance with a detection signal output from the environmentaltemperature detecting portion.
 6. The polar modulating circuit accordingto claim 1, wherein the phase compensating portion adjusts the amplitudeof the address designation signal or the phase-modulated signal input inaccordance with a transmission output power.
 7. The polar modulatingcircuit according to claim 1, wherein the phase compensating portionadjusts the amplitude of the address designation signal or thephase-modulated signal input in accordance with a frequency of an inputsignal of the amplifying portion.
 8. The polar modulating circuitaccording to claim 1, further comprising an environmental temperaturedetecting portion, wherein the phase compensating portion adjusts theamplitude of the address designation signal or the phase-modulatedsignal input in accordance with a detection signal output from theenvironmental temperature detecting portion.
 9. An integrated circuit onwhich a polar modulating circuit according to claim 1 is mounted.
 10. Atransmitting apparatus comprising a polar modulating circuit accordingto claim
 1. 11. A transmitting apparatus comprising an integratedcircuit according to claim
 9. 12. A polar modulating method comprising:producing an amplitude signal and a phase signal from a basebandquadrature signal that is produced from transmission data; storingpredistortion distortion compensating process data for a predeterminedphase correcting process in a memory; outputting a phase correctionsignal for correcting the phase signal from the memory; producing anamplitude-modulated signal based on the amplitude signal; producing aphase-modulated signal in a radio-frequency band based on a phase signalcorrected by using the phase correction signal output from the memoryportion; inputting the phase-modulated signal as an input high-frequencysignal and inputting the amplitude-modulated signal as a control signal,thereby producing transmission data in the radio-frequency band; andperforming the phase compensation by adjusting amplitude of an addressdesignation signal when the phase correction signal is output from thememory or adjusting an amplitude of the phase-modulated signal input tothe amplifying portion as the input high-frequency signal.